feat: resilient delivery, live progress visibility, TG-side answering, /stop /mission /new

Delivery & visibility:
- per-chunk retry with capped backoff on rich/HTML sends; rich failure now
  falls back to HTML instead of dropping the reply
- typing heartbeat: refresh sendChatAction every 4s for the whole turn
  (a single action expires in ~5s, long turns looked dead)
- turn/end error / abort / crash-recovery notices reach Telegram
  (API failures were previously invisible)
- tool/call progress summaries, tool/result failure notices, todo progress
- thinking indicator (one notice per reasoning phase, status only)
- notices prefixed '> ' render as Telegram blockquotes; plain-text fallback
- non-text messages get a hint instead of being silently dropped
- busy feedback: a followup queued mid-turn gets an explicit ack

TG-side answering (dual-path race; UI path untouched, first answer wins):
- ask_user_question questions render with letter options on TG; reply A /
  [A] / A,B (multi) / free text / '1: A' per-line for multi-question
- approval requests (approval/request waterfall) answerable from TG:
  [A] allow once / [B] reject; /cancel closes only the TG side

Commands: /stop (cancel current turn), /mission (todo snapshot + busy state),
/new (create a session in the current workspace and attach)

Persistence: chat→session bindings stored at $DSH_HOME/
telegram-channel-bindings.json (override: DSH_TELEGRAM_BINDINGS_FILE) and
restored on start — hot reloads and restarts no longer drop attachments.

Host seams without public surface yet are reached with documented structural
casts (userQuestions provider wrap, approval/request waterfall).

Tests: 41/41 pass. Two pre-existing environment failures in bridge.test.ts
(/last history mirror, assistant mirror) now pass: the former was fixed by
the rich→HTML fallback, the latter needed an event-loop flush after the
(void) listener call since resilient delivery lengthens the chain.

tests/bridge.test.ts

@@ -298,6 +298,10 @@ test('callback bind then plain text followups live agent; mirror assistant to ch
       data: { message: { content: [{ type: 'text', text: 'reply from agent' }] } },
     },
   )
+  // Delivery is intentionally resilient now (per-chunk retry + rich→HTML
+  // fallback), which lengthens the async microtask chain past this listener's
+  // void return — flush the event loop before asserting.
+  await new Promise((r) => setTimeout(r, 0))
   assert.ok(sent.some((m) => m.text.includes('reply from agent') || m.text.includes('reply')))
 
   await bridge.stop()