refactor(01-04): remove stale 'Plan 04 wires this' comments now that it's wired

- Update module header to list port keepalive + OFFSCREEN_READY among
  the module's owned responsibilities (no longer "wired by Plan 04")
- Replace 'Plan 04 owns the ping loop' on PORT_NAME with the actual
  D-17 + Pattern 5 citation
- Replace 'Plan 04 fills the lifecycle' on keepalivePort with its
  D-17 + Pattern 5 role

Pure comment cleanup — no behavior change. All 9 tests still GREEN.

src/offscreen/recorder.ts

@@ -2,8 +2,8 @@
 // offscreen/index.ts and the inline string in vite.config.ts:13-216).
 // Owns: getDisplayMedia capture, MediaRecorder lifecycle, in-memory ring
 // buffer with WebM-header retention + 30 s age trim, codec strict-mode,
-// track.onended cleanup. Port keepalive + OFFSCREEN_READY handshake are
-// wired by Plan 04 in the matching wave-1 lane.
+// track.onended cleanup, long-lived port keepalive (D-17), and the
+// OFFSCREEN_READY handshake (Pattern 4).
 
 import { OffscreenLogger } from '../shared/logger';
 import type { Message, VideoChunk } from '../shared/types';
@@ -13,7 +13,7 @@ export const VIDEO_BUFFER_DURATION_MS = 30_000;    // 30 секунд
 const VIDEO_MIME = 'video/webm;codecs=vp9';        // D-20 strict — no fallback
 const VIDEO_BITRATE = 400_000;                     // CON-video-codec
 const TIMESLICE_MS = 2_000;                        // SPEC §4.1
-const PORT_NAME = 'video-keepalive';               // Plan 04 owns the ping loop
+const PORT_NAME = 'video-keepalive';               // long-lived port name (D-17, Pattern 5)
 const PORT_PING_MS = 25_000;                       // < 30 s SW idle threshold
 const PORT_RECONNECT_MS = 290_000;                 // pre-empt the ~5 min port cap (Pitfall 4)
 
@@ -24,7 +24,7 @@ let videoRecorder: MediaRecorder | null = null;    // renamed from 'mediaRecorde
 let mediaStream: MediaStream | null = null;
 let videoBuffer: VideoChunk[] = [];
 let firstChunkSaved = false;
-let keepalivePort: chrome.runtime.Port | null = null;     // Plan 04 fills the lifecycle
+let keepalivePort: chrome.runtime.Port | null = null;     // long-lived SW keepalive (D-17, Pattern 5)
 
 // ─── Кольцевой буфер (pure functions — testable in Node) ────────────────