Merge development into main for the v1.0.0 release

Ships 45 commits: the tool permission and MCP repo workflow tools, web search, Google sign-in, the admin console, branding sync, and the new app version + public changelog. Introduces Sigitsi::VERSION (1.0.0), surfaced in the footer and at /changelog. Deploy note: the delta includes the add_oauth_provider_to_users migration. The post-receive hook does not reliably migrate, so run it by hand and restart Puma after pushing to prod.