docs(google-calendar): setup guide, Telegram configuration and architecture notes

Spec: the unverified-app screen is described in text; open question 1 resolved (full calendar scope); status implemented.

README.md

@@ -17,6 +17,7 @@ Claude Code as a model provider without an API key.
 | Anthropic Messages API provider | `extensions/Volcanic.AgenticCore.Extensions.Anthropic` | `ANTHROPIC_API_KEY` |
 | OpenAI-compatible provider | `extensions/Volcanic.AgenticCore.Extensions.OpenAI` | OpenAI, OpenRouter, Groq, Ollama, llama.cpp, vLLM |
 | Claude Code (subscription) provider | `extensions/Volcanic.AgenticCore.Extensions.ClaudeCode` (+ `.Bridge`) | Spawns `claude -p`, MCP "proposal" bridge |
+| Google Calendar (tool + connect commands) | `extensions/Volcanic.AgenticCore.Extensions.GoogleCalendar` | `GOOGLE_CLIENT_ID`, `GOOGLE_CLIENT_SECRET`; one account per chat |
 | Telegram bot | `hosts/Volcanic.AgenticCore.Telegram` | Chat with the agent from Telegram; long polling, Claude Code, allow-list |
 | Reference headless host | `samples/Volcanic.AgenticCore.Sample.Headless` | Prompt in, JSON events out |
 | Tests | `tests/` | xunit; no test calls a paid API |
@@ -67,6 +68,7 @@ await session.PromptAsync("Explain this repository");
 - [Writing extensions](docs/extensions.md): tools, commands, lifecycle hooks, providers, message injection, discovery.
 - [Providers and models](docs/providers.md): model keys, authentication, the built-in provider extensions.
 - [Telegram bot](docs/telegram-bot.md): setup, commands, security, connection recovery.
+- [Google Calendar](docs/google-calendar.md): Google Cloud setup, connecting a chat, token storage, time zones.
 - [Building a UI (Telegram guide)](docs/ui-integration.md): how to put a chat front end on the core.
 - [Claude Code provider](docs/claude-code-provider.md): requirements, how the bridge works, limits, the doctor
   command, automatic re-login when the subscription session expires.