feat(telegram): add disable_topic_auto_rename gateway flag

When Hermes auto-titles a session in a Telegram DM topic it currently
renames the topic itself to the generated title. That works for
operator-managed lanes (extra.dm_topics) but is disruptive for
ad-hoc Threaded-Mode topics that users name by hand — every first
exchange overwrites their chosen title.

Add gateway.platforms.telegram.extra.disable_topic_auto_rename (default
False, preserving prior behaviour). When set, both
_schedule_telegram_topic_title_rename and the underlying
_rename_telegram_topic_for_session_title short-circuit before touching
the Telegram API. Internal session titles (sessions list, TUI) keep
working unchanged.

Also bridge the legacy top-level telegram.disable_topic_auto_rename key
through to gateway.platforms.telegram.extra so users on the older
config layout don't have to migrate to enable it.

- Tests cover the runtime flag, the scheduling entry-point, and string
  truthiness coercion for YAML-loaded values.
- Docs updated in messaging/telegram.md with an example block.

website/docs/user-guide/messaging/telegram.md

@@ -497,6 +497,18 @@ Every topic gets its own conversation history, model state, tool execution, and
 
 When Hermes generates a session title for a topic (via the auto-title pipeline, after the first exchange), the Telegram topic itself is renamed to match — e.g. "New Topic" becomes "Database migration plan". The rename is best-effort: failures are logged but don't break the session.
 
+To disable this and keep your manually-chosen topic names untouched, set:
+
+```yaml
+gateway:
+  platforms:
+    telegram:
+      extra:
+        disable_topic_auto_rename: true
+```
+
+When this flag is on, Hermes still generates an internal session title (used by `hermes sessions`, the TUI, etc.) but never edits the Telegram topic name. Useful when you organise topics by hand under BotFather Threaded Mode and don't want every first reply to overwrite the title.
+
 ### `/new` inside a topic
 
 Resets the current topic's session (new session ID, fresh history) without touching other topics. Hermes replies with a reminder that for parallel work, creating another topic (via **All Messages**) is usually what you want.
@@ -530,6 +542,7 @@ Shows the current topic's binding: session title, session ID, and hints for `/ne
 - Each inbound DM message looks up its `(chat_id, thread_id)` binding. If present, the lookup routes the message to the bound session via `SessionStore.switch_session()` so the session-key-to-session-id mapping stays consistent on disk
 - `/new` inside a topic rewrites the binding row to point at the new session ID, so the next message stays on the fresh session
 - Topics declared in `extra.dm_topics` are **never auto-renamed** — the operator-chosen name is preserved even when multi-session mode is enabled
+- Set `extra.disable_topic_auto_rename: true` to turn off auto-rename for **all** topics in the chat (ad-hoc topics created via Threaded Mode included)
 - The General (pinned top) topic in a forum-enabled DM is treated as the root lobby, regardless of whether Telegram delivers its messages with `message_thread_id=1` or with no thread_id
 - Root-lobby reminders are rate-limited to one message per 30 seconds per chat — a user who forgets topic mode is on and types ten prompts in the root won't get ten replies
 - BotFather setup screenshots are rate-limited to one send per 5 minutes per chat — repeated `/topic` attempts while Threads Settings are still disabled won't re-upload the same image