fix: add comprehensive type annotations for mypy

- database.py: add type hints for Path, Flask, Any, BaseException
- pki.py: add assertions to narrow Optional types after has_ca() checks
- routes.py: annotate config values to avoid Any return types
- api/__init__.py: use float for cleanup timestamps (time.time())
- __init__.py: remove unused return from setup_rate_limiting

app/api/__init__.py

@@ -9,10 +9,10 @@ bp = Blueprint("api", __name__)
 
 # Thread-safe cleanup scheduling
 _cleanup_lock = threading.Lock()
-_cleanup_times = {
-    "pastes": 0,
-    "hashes": 0,
-    "rate_limits": 0,
+_cleanup_times: dict[str, float] = {
+    "pastes": 0.0,
+    "hashes": 0.0,
+    "rate_limits": 0.0,
 }
 _CLEANUP_INTERVALS = {
     "pastes": 3600,  # 1 hour
@@ -25,7 +25,7 @@ def reset_cleanup_times() -> None:
     """Reset cleanup timestamps. For testing only."""
     with _cleanup_lock:
         for key in _cleanup_times:
-            _cleanup_times[key] = 0
+            _cleanup_times[key] = 0.0
 
 
 @bp.before_request