feat(01-03): add OffscreenLogger and clean up shared types

- Add PortMessageType and PortMessage interface to src/shared/types.ts
  for the long-lived port (offscreen ↔ SW; D-17 / Plan 04 wires the
  ping loop + REQUEST_BUFFER / BUFFER traffic).
- Remove 'VIDEO_CHUNK' and 'VIDEO_CHUNK_SAVED' from MessageType union
  (per D-19 — chunks no longer travel via chrome.runtime.sendMessage;
  the IndexedDB SW-side plumbing is the audit P0 #2 broken path).
- OffscreenLogger class was already added alongside Task 2 because
  recorder.ts imports it at module top.

Inline SW cleanup (Rule 3 — blocking dependency, plan acceptance gates
on `npx tsc --noEmit` exit 0):
- Remove src/background/index.ts VIDEO_CHUNK + VIDEO_CHUNK_SAVED case
  branches (refs to deleted union members).
- Remove now-unreferenced loadChunkFromIndexedDB / openIndexedDB
  (only reachable from the deleted VIDEO_CHUNK_SAVED branch).
- Remove now-unreferenced addVideoChunkFromBlob / cleanupVideoBuffer
  / firstChunkSaved / VIDEO_BUFFER_DURATION_MS constant (the SW-side
  ring buffer now lives in src/offscreen/recorder.ts per D-16).
- Keep SW-side `videoBuffer: VideoChunk[] = []` as a placeholder; Plan
  04 wires it to fetch from offscreen over the keepalive port. The
  remaining `getVideoBuffer` + `saveArchive` callers continue to
  compile against the empty array until Plan 04 lands.
- Plan 05 owns the broader SW shell cleanup.

Verification (post-commit):
- npx vitest run tests/offscreen/ring-buffer.test.ts tests/offscreen/codec-check.test.ts → 6/6 PASS
- npx tsc --noEmit → exit 0

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

src/shared/types.ts

@@ -13,8 +13,6 @@ export type MessageType =
   | 'START_RECORDING'
   | 'STOP_RECORDING'
   | 'RECORDING_ERROR'
-  | 'VIDEO_CHUNK'
-  | 'VIDEO_CHUNK_SAVED'
   | 'OFFSCREEN_READY';
 
 export interface Message<T = any> {
@@ -23,6 +21,17 @@ export interface Message<T = any> {
   tabId?: number;
 }
 
+// Типы сообщений в long-lived port (offscreen ↔ SW; D-17 / Plan 04)
+export type PortMessageType =
+  | 'PING'
+  | 'REQUEST_BUFFER'
+  | 'BUFFER';
+
+export interface PortMessage {
+  type: PortMessageType;
+  chunks?: VideoChunk[];
+}
+
 // Видеобуфер
 export interface VideoChunk {
   data: Blob;