feat: switch notification backend from Redis to Firestore

- Refactor FirestoreNotificationBackend to use time-gated window
  (window_hours) instead of notified_by_agent status filtering;
  mark_as_notified is now a no-op (agent is awareness-only).
- Update agent.py to instantiate FirestoreNotificationBackend using the
  shared firestore_db client instead of RedisNotificationBackend.
- Remove redis_host/redis_port settings from config.py; add
  notifications_collection_path, max_to_notify, and window_hours.
- Move redis/json imports inside RedisNotificationBackend methods so
  redis is only required if that backend is explicitly instantiated.
- Add utility scripts for checking and registering notifications.
- Add google-cloud-firestore dependency to pyproject.toml.

uv.lock

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+
 [[package]]
 name = "referencing"
 version = "0.37.0"
@@ -1926,6 +1936,7 @@ dependencies = [
     { name = "google-cloud-firestore" },
     { name = "google-genai" },
     { name = "pydantic-settings", extra = ["yaml"] },
+    { name = "redis" },
 ]
 
 [package.dev-dependencies]
@@ -1944,6 +1955,7 @@ requires-dist = [
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     { name = "google-genai", specifier = ">=1.64.0" },
     { name = "pydantic-settings", extras = ["yaml"], specifier = ">=2.13.1" },
+    { name = "redis", specifier = ">=5.0" },
 ]
 
 [package.metadata.requires-dev]