Stage 17 #2: Connecting indicator + auto-retry, instead of red toasts

Connectivity failures become state, not a toast on every attempt. A global online
signal (lib/connection.svelte.ts) flips on a transport unavailable / rate_limited and
on the live stream's drop, driving a pure-CSS header spinner + 'Connecting…' in place
of the title and softly disabling the in-game server actions (commit / exchange / pass
/ hint; local board/rack/reset stay live).

- transport: exec auto-retries with capped exponential backoff — every op on a
  rate-limit (rejected before processing, safe), reads only on unavailable (a mutation
  is never blindly re-sent, to avoid double-applying one whose response was lost; its
  button is disabled while offline so the player re-issues on reconnect). A reachability
  watcher (profile.get probe) and any successful traffic clear the signal.
- the old red error.unavailable toast is gone (handleError suppresses connection codes;
  the indicator replaces it). A server-data screen still opens with the spinner and
  fills on reconnect (global indicator + read auto-retry), so navigation is never dead.
- pure retry policy unit-tested (retry.ts); a mock-only window.__conn hook drives a
  Chromium+WebKit e2e (indicator shows offline, the action disables, both clear on
  reconnect). Full suite + build green.
- docs: ARCHITECTURE transport note, FUNCTIONAL (+ _ru), PLAN tracker (incl. #1 — the
  bot already drains all updates, no change).

Also records #1 as investigated/no-change in PLAN. Other server-action buttons (chat
send, profile save, …) still degrade to a safe no-op offline; visual disable is easy to
extend.

PLAN.md

@@ -1437,6 +1437,28 @@ provided cert) at the contour caddy; prod VPN; rollback.
       connector. The backend resolves the mover's display name (the score line and result are
       built per recipient). Covered by notify round-trip, emit, connector-render (en/ru) and
       routing tests.
+    - **No-op drain of all bot updates (#1, investigated — no change):** confirmed the Telegram bot
+      already long-polls and the library advances the offset for every delivered update (the default
+      handler no-ops anything but `/start`), so the queue never piles up. Telegram withholds only
+      `message_reaction` / `message_reaction_count` / `chat_member` by default, and — being
+      unrequested — those never queue either. Owner chose to leave `allowed_updates` at the default
+      (zero risk) rather than hand-maintain a full whitelist (a wrong/stale type would break
+      `getUpdates` entirely); a specific type will be requested when a concrete handler needs it.
+    - **Reconnect UX — "Connecting…" + soft-disable (#2, shipped):** connectivity failures became
+      **state, not toasts**. A global `online` signal (`lib/connection.svelte.ts`) flips on a
+      transport `unavailable` / `rate_limited` (and on the live stream's drop), driving a pure-CSS
+      header **spinner + "Connecting…"** in place of the title and softly disabling the in-game
+      server actions (commit / exchange / pass / hint; local board/rack/reset stay live). The
+      transport (`exec`) **auto-retries with capped backoff** — every op on a rate-limit, **reads
+      only** on `unavailable` (mutations are not blindly re-sent; their buttons are disabled while
+      offline, so the player re-issues on reconnect — the idempotency caveat the owner accepted). A
+      reachability **watcher** (`profile.get` probe) and any successful traffic clear the signal; the
+      old red `error.unavailable` toast is gone (the indicator replaces it). A server-data screen
+      still **opens with the spinner** and fills on reconnect (global indicator + read auto-retry),
+      so navigation is never dead. Pure policy unit-tested (`retry.ts`); a mock-only `window.__conn`
+      hook drives a Chromium+WebKit e2e (indicator appears offline, the action disables, both clear
+      on reconnect). Other server-action buttons (chat send, profile save, …) are not yet visually
+      disabled but degrade to a safe no-op (the suppressed toast + indicator) — easy to extend.
 
 ## Deferred TODOs (cross-stage)