feat: normalized external-agent status (#10 scoped) (v2.7.6)

Scoped half of boocode_code_review_v2 §1 #10 — publish the agent status
BooCoder already observes (the config-injection notify-hook is the documented
follow-on, clean-room from superset ELv2).

- agent_status_updated WS frame (working|blocked|idle|error), server+web parity.
- Published from the dispatcher's turn boundaries (warm-acp/opencode/sdk/pty:
  working at start, idle/error at end) + the permission flow (blocked/working).
  Best-effort, never breaks a turn.
- Clean-room normalizeAgentEvent helper (superset's vendor-event -> Start/blocked
  /Stop collapse, event names as facts) + 25 tests — reused by the follow-on.
- AgentComposerBar status dot (distinct from the WS-liveness dot), tracked per
  (chat,agent) by a useAgentStatus map in CoderPane.

Built by 2 parallel agents vs a pinned frame contract. Server 545 + coder 294
tests passing (25 new); web tsc + builds clean; ws-frames parity green. Clears
the actionable review backlog (#1/#3/#4/#6-#12). Builds on v2.7.5.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/web/src/hooks/useSessionStream.ts

@@ -189,6 +189,12 @@ function applyFrame(state: State, frame: WsFrame): State {
       // duplicating async work inside a synchronous reducer.
       return state;
     }
+    case 'agent_status_updated': {
+      // agent-status-normalize (#10): coder-only frame consumed by CoderPane's
+      // own WS handler, not BooChat's native message reducer. No-op here to keep
+      // TS exhaustiveness satisfied (native sessions never emit it).
+      return state;
+    }
   }
 }