feat(media): MediaStore for image persistence and cleanup

Task 8 of the slice plan. Saves clipboard PNG/JPEG bytes under
{profileDir}/media/{noteId}/{uuid}.{ext} with mkdir -p semantics,
returns relPath/mime/bytes for the repository row, supports
deleteNoteDirectory (used by note delete + GC) and listNoteDirs
(used by media GC to find orphans).

Verification: `npx vitest run tests/unit/MediaStore.test.ts`
4 passed.

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

src/main/services/MediaStore.ts

@@ -0,0 +1,37 @@
+import { mkdir, writeFile, rm, readdir } from 'node:fs/promises';
+import { join } from 'node:path';
+import { v4 as uuidv4 } from 'uuid';
+
+export interface SavedMedia {
+  relPath: string;
+  mime: string;
+  bytes: number;
+}
+
+export class MediaStore {
+  constructor(private profileDir: string) {}
+
+  async saveImage(noteId: string, bytes: Buffer, mime: string): Promise<SavedMedia> {
+    const dir = join(this.profileDir, 'media', noteId);
+    await mkdir(dir, { recursive: true });
+    const ext = mime === 'image/png' ? 'png' : mime === 'image/jpeg' ? 'jpg' : 'bin';
+    const filename = `${uuidv4()}.${ext}`;
+    await writeFile(join(dir, filename), bytes);
+    return { relPath: `media/${noteId}/${filename}`, mime, bytes: bytes.length };
+  }
+
+  async deleteNoteDirectory(noteId: string): Promise<void> {
+    await rm(join(this.profileDir, 'media', noteId), { recursive: true, force: true });
+  }
+
+  async listNoteDirs(): Promise<string[]> {
+    const root = join(this.profileDir, 'media');
+    try {
+      const entries = await readdir(root, { withFileTypes: true });
+      return entries.filter((e) => e.isDirectory()).map((e) => e.name);
+    } catch (err) {
+      if ((err as NodeJS.ErrnoException).code === 'ENOENT') return [];
+      throw err;
+    }
+  }
+}

tests/unit/MediaStore.test.ts

@@ -0,0 +1,43 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+import { mkdtempSync, readFileSync, existsSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { MediaStore } from '@main/services/MediaStore.js';
+
+describe('MediaStore', () => {
+  let tmp: string;
+  let store: MediaStore;
+
+  beforeEach(() => {
+    tmp = mkdtempSync(join(tmpdir(), 'inkling-media-'));
+    store = new MediaStore(tmp);
+  });
+
+  it('saves a png under media/{noteId}/', async () => {
+    const bytes = Buffer.from('\x89PNG\r\n\x1a\n' + 'A'.repeat(100));
+    const saved = await store.saveImage('note-123', bytes, 'image/png');
+    expect(saved.relPath.startsWith('media/note-123/')).toBe(true);
+    expect(saved.relPath.endsWith('.png')).toBe(true);
+    expect(saved.bytes).toBe(bytes.length);
+    expect(readFileSync(join(tmp, saved.relPath)).equals(bytes)).toBe(true);
+  });
+
+  it('saves multiple images with unique filenames', async () => {
+    const bytes = Buffer.from('abc');
+    const a = await store.saveImage('n', bytes, 'image/png');
+    const b = await store.saveImage('n', bytes, 'image/png');
+    expect(a.relPath).not.toBe(b.relPath);
+  });
+
+  it('deleteNoteDirectory removes the note dir', async () => {
+    await store.saveImage('note-x', Buffer.from('abc'), 'image/png');
+    await store.deleteNoteDirectory('note-x');
+    expect(existsSync(join(tmp, 'media/note-x'))).toBe(false);
+  });
+
+  it('listNoteDirs returns dir names', async () => {
+    await store.saveImage('alpha', Buffer.from('a'), 'image/png');
+    await store.saveImage('beta', Buffer.from('b'), 'image/png');
+    expect((await store.listNoteDirs()).sort()).toEqual(['alpha', 'beta']);
+  });
+});