Add contributing guidelines, feature flag utilities, and route integrity tests

CONTRIBUTING.md

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+# Contributing to SaaS-PDF
+
+## Safety Rules
+
+These rules are **non-negotiable**. Every PR must comply.
+
+### 1. Never Delete Existing Routes
+
+All routes are registered in `frontend/src/config/routes.ts`. This file is the canonical source of truth. The route safety test (`routes.test.ts`) verifies that every registered route exists in `App.tsx`.
+
+- **Adding a route:** Append to `routes.ts` → add `<Route>` in `App.tsx`
+- **Removing a route:** ❌ NEVER. Deprecate by redirecting instead.
+
+### 2. Never Modify Existing Working Tools
+
+Each tool lives in its own file under `frontend/src/components/tools/`. Do not change a tool's:
+
+- Public API (props, accepted file types, output format)
+- Route path
+- Backend endpoint it calls
+
+If you need to change behavior, add a new option behind a feature flag.
+
+### 3. Never Break Existing Tests
+
+Run the full test suites before pushing:
+
+```bash
+# Frontend
+cd frontend && npx vitest run
+
+# Backend
+cd backend && python -m pytest tests/ -q
+```
+
+If a test fails after your change, **fix your code**, not the test — unless the test itself is wrong (and you explain why in the PR).
+
+### 4. Add New Functionality in Isolated Modules
+
+- New tools → new file under `components/tools/`
+- New pages → new file under `pages/`
+- New backend routes → new file or append to existing route file
+- New services → new file under `services/` or `utils/`
+
+Never add new logic inline to existing tool components. Keep changes isolated so they can be reverted independently.
+
+### 5. Use Feature Flags When Needed
+
+#### Backend
+
+Feature flags are defined in `backend/config/__init__.py`:
+
+```python
+FEATURE_EDITOR = os.getenv("FEATURE_EDITOR", "true").lower() == "true"
+```
+
+Check them in routes:
+
+```python
+from flask import current_app
+if not current_app.config.get("FEATURE_EDITOR"):
+    return jsonify(error="Feature disabled"), 403
+```
+
+#### Frontend
+
+Feature flags are defined in `frontend/src/config/featureFlags.ts`:
+
+```typescript
+import { isFeatureEnabled } from '@/config/featureFlags';
+
+if (isFeatureEnabled('EDITOR')) {
+  // render the tool
+}
+```
+
+Set via environment variables:
+
+```env
+VITE_FEATURE_EDITOR=true    # enabled (default)
+VITE_FEATURE_OCR=false      # disabled
+```
+
+---
+
+## Development Workflow
+
+### Branch Naming
+
+| Type | Pattern | Example |
+|------|---------|---------|
+| Feature | `feature/tool-name` | `feature/pdf-merger` |
+| Fix | `fix/issue-description` | `fix/ocr-language-flag` |
+| SEO | `feature/seo-*` | `feature/seo-content` |
+
+### PR Checklist
+
+- [ ] No existing routes removed (checked by `routes.test.ts`)
+- [ ] No existing tool components modified (unless bug fix)
+- [ ] All tests pass (`vitest run` + `pytest`)
+- [ ] Build succeeds (`npx vite build`)
+- [ ] New routes added to `routes.ts` registry
+- [ ] New i18n keys added to all 3 language files (en, ar, fr)
+- [ ] Feature flag added if the feature can be disabled
+
+### File Structure Convention
+
+```
+frontend/src/
+├── components/
+│   ├── layout/         # Header, Footer, AdSlot
+│   ├── shared/         # Reusable components (ToolCard, ErrorBoundary)
+│   ├── seo/            # SEOHead, ToolLandingPage, FAQSection
+│   └── tools/          # One file per tool (PdfToWord.tsx, etc.)
+├── config/
+│   ├── routes.ts       # Canonical route registry (NEVER delete entries)
+│   ├── featureFlags.ts # Frontend feature flag reader
+│   ├── seoData.ts      # SEO metadata for all tools
+│   └── toolLimits.ts   # File size limits
+├── hooks/              # Custom React hooks
+├── i18n/               # Translation files (en.json, ar.json, fr.json)
+├── pages/              # Page components (HomePage, AboutPage, etc.)
+├── services/           # API clients, analytics
+├── stores/             # Zustand stores
+└── utils/              # Pure utility functions (seo.ts, etc.)
+```

frontend/src/config/featureFlags.ts

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+/**
+ * Feature flag utilities for the frontend.
+ *
+ * Feature flags are read from VITE_FEATURE_* environment variables.
+ * When a flag is absent or set to "true", the feature is ENABLED (opt-out model).
+ * Set a flag to "false" to disable a feature.
+ *
+ * Usage:
+ *   import { isFeatureEnabled } from '@/config/featureFlags';
+ *   if (isFeatureEnabled('EDITOR')) { ... }
+ */
+
+type FeatureName = 'EDITOR' | 'OCR' | 'REMOVEBG';
+
+/**
+ * Check whether a feature is enabled.
+ * Defaults to `true` if the env var is not set.
+ */
+export function isFeatureEnabled(feature: FeatureName): boolean {
+  const value = import.meta.env[`VITE_FEATURE_${feature}`];
+  if (value === undefined || value === '') return true; // enabled by default
+  return value.toLowerCase() !== 'false';
+}

frontend/src/config/routes.test.ts

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+import { describe, it, expect } from 'vitest';
+import { readFileSync } from 'fs';
+import { resolve, dirname } from 'path';
+import { fileURLToPath } from 'url';
+import { ALL_ROUTES } from '@/config/routes';
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = dirname(__filename);
+
+/**
+ * SAFETY TEST — Route Integrity
+ *
+ * Ensures that every route in the canonical registry (routes.ts)
+ * has a matching <Route path="..."> in App.tsx.
+ *
+ * If this test fails it means either:
+ *  1. A route was removed from App.tsx (NEVER do this)
+ *  2. A route was added to routes.ts but not yet wired in App.tsx
+ */
+describe('Route safety', () => {
+  const appSource = readFileSync(
+    resolve(__dirname, '../App.tsx'),
+    'utf-8'
+  );
+
+  // Extract all path="..." values from <Route> elements
+  const routePathRegex = /path="([^"]+)"/g;
+  const appPaths = new Set<string>();
+  let match: RegExpExecArray | null;
+  while ((match = routePathRegex.exec(appSource)) !== null) {
+    if (match[1] !== '*') appPaths.add(match[1]);
+  }
+
+  it('App.tsx contains routes for every entry in the route registry', () => {
+    const missing = ALL_ROUTES.filter((r) => !appPaths.has(r));
+    expect(missing, `Missing routes in App.tsx: ${missing.join(', ')}`).toEqual([]);
+  });
+
+  it('route registry is not empty', () => {
+    expect(ALL_ROUTES.length).toBeGreaterThan(0);
+  });
+
+  it('no duplicate routes in the registry', () => {
+    const seen = new Set<string>();
+    const duplicates: string[] = [];
+    for (const route of ALL_ROUTES) {
+      if (seen.has(route)) duplicates.push(route);
+      seen.add(route);
+    }
+    expect(duplicates, `Duplicate routes: ${duplicates.join(', ')}`).toEqual([]);
+  });
+});

frontend/src/config/routes.ts

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+/**
+ * Canonical route registry — single source of truth for all application routes.
+ *
+ * SAFETY RULE: Never remove a route from this list.
+ * New routes may only be appended. The route safety test
+ * (routes.test.ts) will fail if any existing route is deleted.
+ */
+
+// ─── Page routes ─────────────────────────────────────────────────
+export const PAGE_ROUTES = [
+  '/',
+  '/about',
+  '/account',
+  '/forgot-password',
+  '/reset-password',
+  '/privacy',
+  '/terms',
+  '/contact',
+] as const;
+
+// ─── Tool routes ─────────────────────────────────────────────────
+export const TOOL_ROUTES = [
+  // PDF Tools
+  '/tools/pdf-to-word',
+  '/tools/word-to-pdf',
+  '/tools/compress-pdf',
+  '/tools/merge-pdf',
+  '/tools/split-pdf',
+  '/tools/rotate-pdf',
+  '/tools/pdf-to-images',
+  '/tools/images-to-pdf',
+  '/tools/watermark-pdf',
+  '/tools/protect-pdf',
+  '/tools/unlock-pdf',
+  '/tools/page-numbers',
+  '/tools/pdf-editor',
+  '/tools/pdf-flowchart',
+  '/tools/pdf-to-excel',
+  '/tools/remove-watermark-pdf',
+  '/tools/reorder-pdf',
+  '/tools/extract-pages',
+
+  // Image Tools
+  '/tools/image-converter',
+  '/tools/image-resize',
+  '/tools/compress-image',
+  '/tools/ocr',
+  '/tools/remove-background',
+
+  // Convert Tools
+  '/tools/html-to-pdf',
+
+  // AI Tools
+  '/tools/chat-pdf',
+  '/tools/summarize-pdf',
+  '/tools/translate-pdf',
+  '/tools/extract-tables',
+
+  // Other Tools
+  '/tools/qr-code',
+  '/tools/video-to-gif',
+  '/tools/word-counter',
+  '/tools/text-cleaner',
+] as const;
+
+// ─── All routes combined ─────────────────────────────────────────
+export const ALL_ROUTES = [...PAGE_ROUTES, ...TOOL_ROUTES] as const;
+
+export type PageRoute = (typeof PAGE_ROUTES)[number];
+export type ToolRoute = (typeof TOOL_ROUTES)[number];
+export type AppRoute = (typeof ALL_ROUTES)[number];