refactor(tools): decorator-based tool registry replaces monolithic tools.py

Split 2566-line tools.py into a tools/ package with @tool decorator
registration. Each tool's schema, metadata, and implementation live
together. Briefing eligibility is now a briefing=True flag instead of
a separate frozenset allowlist. Conditional inclusion (CalDAV, SearXNG)
uses requires= metadata. Public API (get_tools_for_user, execute_tool)
unchanged.

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

src/fabledassistant/services/tools/__init__.py

@@ -0,0 +1,32 @@
+"""Tool registry package.
+
+Importing this package loads all tool modules (triggering ``@tool``
+decorator registration) and re-exports the public API that the rest
+of the app depends on.
+"""
+
+# Import every tool module so their @tool decorators run at import time.
+# Order does not matter — registration is additive.
+from fabledassistant.services.tools import (  # noqa: F401
+    calendar,
+    entities,
+    notes,
+    profile,
+    projects,
+    rag,
+    rss,
+    tasks,
+    weather,
+    web,
+)
+from fabledassistant.services.tools._registry import (
+    execute_tool,
+    get_briefing_tools,
+    get_tools_for_user,
+)
+
+__all__ = [
+    "execute_tool",
+    "get_briefing_tools",
+    "get_tools_for_user",
+]