feat: API key routes, search endpoint, conversation type wiring

- GET/POST/DELETE /api/api-keys blueprint registered
- GET /api/search?q=&content_type=&limit= semantic search endpoint
- create_conversation gains conversation_type param (default "chat")
- cleanup_old_conversations excludes mcp type from retention sweep
- POST /api/chat/conversations accepts conversation_type body field

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_search_route.py

@@ -0,0 +1,18 @@
+"""Unit tests for the search route parameter mapping."""
+from fabledassistant.routes.search import _content_type_to_is_task
+
+
+def test_content_type_note():
+    assert _content_type_to_is_task("note") is False
+
+
+def test_content_type_task():
+    assert _content_type_to_is_task("task") is True
+
+
+def test_content_type_all():
+    assert _content_type_to_is_task("all") is None
+
+
+def test_content_type_unknown_defaults_to_all():
+    assert _content_type_to_is_task("unknown") is None