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>
