fix: Add scrollable container to ToolSelectorModal for small screens

- Add max-h-[90vh] and flex-col to modal content container
- Wrap tools grid in max-h-[50vh] overflow-y-auto container
- Add overscroll-contain for smooth scroll behavior on mobile
- Fixes issue where 21 PDF tools overflow viewport on small screens

backend/app/services/guest_budget_service.py

@@ -0,0 +1,86 @@
+"""Guest demo budget enforcement.
+
+Anonymous visitors get a small usage budget tracked by IP address
+via Redis (with Flask session fallback).  The budget prevents abuse
+of expensive tools before the download-gate forces registration.
+"""
+
+import os
+from flask import request, session
+
+from app.services.credit_config import GUEST_DEMO_BUDGET, GUEST_DEMO_TTL_HOURS
+
+_TTL_SECONDS = GUEST_DEMO_TTL_HOURS * 3600
+
+
+# ── Redis helpers ──────────────────────────────────────────────
+def _get_redis():
+    try:
+        import redis
+        redis_url = os.getenv("REDIS_URL", "redis://localhost:6379/0")
+        return redis.Redis.from_url(redis_url, decode_responses=True)
+    except Exception:
+        return None
+
+
+def _guest_redis_key(ip: str) -> str:
+    return f"guest_demo:{ip}"
+
+
+def _get_client_ip() -> str:
+    """Return the best-effort client IP for rate tracking."""
+    forwarded = request.headers.get("X-Forwarded-For", "")
+    if forwarded:
+        return forwarded.split(",")[0].strip()
+    return request.remote_addr or "unknown"
+
+
+# ── Public API ─────────────────────────────────────────────────
+
+def get_guest_remaining() -> int:
+    """Return how many demo operations the current guest has left."""
+    ip = _get_client_ip()
+    r = _get_redis()
+
+    if r is not None:
+        try:
+            used = r.get(_guest_redis_key(ip))
+            if used is None:
+                return GUEST_DEMO_BUDGET
+            return max(0, GUEST_DEMO_BUDGET - int(str(used)))
+        except Exception:
+            pass
+
+    # Fallback: Flask session
+    used = session.get("guest_demo_used", 0)
+    return max(0, GUEST_DEMO_BUDGET - used)
+
+
+def record_guest_usage() -> None:
+    """Increment the guest demo counter for the current visitor."""
+    ip = _get_client_ip()
+    r = _get_redis()
+
+    if r is not None:
+        try:
+            key = _guest_redis_key(ip)
+            pipe = r.pipeline()
+            pipe.incr(key)
+            pipe.expire(key, _TTL_SECONDS)
+            pipe.execute()
+            return
+        except Exception:
+            pass
+
+    # Fallback: Flask session
+    session["guest_demo_used"] = session.get("guest_demo_used", 0) + 1
+
+
+def assert_guest_budget_available() -> None:
+    """Raise ValueError if the guest has exhausted their demo budget."""
+    remaining = get_guest_remaining()
+    if remaining <= 0:
+        raise ValueError(
+            "You have used all your free demo tries. "
+            "Create a free account to continue."
+        )