feat(plugins): expose thread_id to plugins (#99)

docs/public-api.md

@@ -183,6 +183,15 @@ Command handlers receive a `CommandContext` with:
 Use `ctx.executor.run_one(...)` or `ctx.executor.run_many(...)` to reuse Takopi's
 engine pipeline. Use `mode="capture"` to collect results and build a custom reply.
 
+`ctx.message` and `ctx.reply_to` are `MessageRef` objects with:
+
+- `channel_id` (`int | str`, chat/channel id)
+- `message_id` (`int | str`, message id)
+- `thread_id` (`int | str | None`; set when the transport supports threads, like Telegram topics)
+- `raw` (transport-specific payload, may be `None`)
+
+Example: key per-thread state by `(ctx.message.channel_id, ctx.message.thread_id)`.
+
 ---
 
 ## TransportRuntime helpers
@@ -228,6 +237,7 @@ async def on_message(...):
         message_id=...,
         text=...,
         reply_to=...,
+        thread_id=...,
     )
     await handle_message(
         exec_cfg,