docs: add v1→v2 action-items analysis + SDK signal probe tool

- docs/v1-vs-v2/: full v1→v2 regression analysis (SUMMARY + 21 per-module
  docs + ACTION-ITEMS rollup with decisions + timezone recreation spec).
- container/agent-runner/scripts/sdk-signal-probe.ts: empirical harness
  used to characterise Claude Agent SDK event/hook/stderr timing for the
  stuck-detection design in item 9.
- src/channels/chat-sdk-bridge.ts: document the conversations Map staleness
  in a code comment; fix deferred to when dynamic group registration lands
  (ACTION-ITEMS item 17).

No runtime behavior change.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/v1-vs-v2/timezone.md

@@ -0,0 +1,27 @@
+# timezone: v1 vs v2
+
+## Scope
+- v1: `src/v1/timezone.ts` (37 LOC), `src/v1/timezone.test.ts` (64 LOC)
+- v2 counterparts: `src/timezone.ts` (37 LOC), `src/timezone.test.ts` (64 LOC)
+
+## Capability map
+
+| v1 behavior | v2 location | Status | Notes |
+|---|---|---|---|
+| `isValidTimezone(tz)` | `src/timezone.ts:5-12` | kept | Byte-identical |
+| `resolveTimezone(tz)` | `src/timezone.ts:17-19` | kept | Byte-identical |
+| `formatLocalTime(utcIso, timezone)` | `src/timezone.ts:26-37` | kept | Byte-identical |
+
+## Tests (byte-identical)
+- `formatLocalTime`: UTC→local display with offset; DST awareness (EDT vs EST); fall back to UTC on invalid tz without throwing
+- `isValidTimezone`: accepts `America/New_York`, `UTC`, `Asia/Tokyo`, `Asia/Jerusalem`; rejects `IST-2`, `XYZ+3`, empty/garbage
+- `resolveTimezone`: returns tz if valid; falls back to UTC on invalid or empty
+
+## Missing from v2
+None — v1 and v2 files are byte-for-byte identical.
+
+## Behavioral discrepancies
+None.
+
+## Worth preserving?
+No action needed — v2 already mirrors v1 exactly. Minimal, correct, no external deps. No cron-time conversions in either version (that logic lived in `task-scheduler.ts`).