feat(share): time-limited share links with cfi-aware imports (#4037)

Add a Share Book feature that generates an expiring HTTPS share URL plus a
parallel readest://share/{token} deep link. Recipients land on /s/{token},
where logged-in users can one-tap "Add to my library" (R2 server-side
byte-copy) and anonymous users download the book or open it in the app.
Sharers manage active links from a dedicated "Manage Shared Links" panel
under user settings.

Highlights:
- 9 new App Router endpoints under /api/share (create, [token], cover,
  og.png, download, download/confirm, import, revoke, list).
- /s landing page with branded next/og chat unfurl image and SSR auth-cookie
  detection so logged-in recipients see "Add to my library" as the primary
  action without layout shift.
- Server-side R2 byte-copy for /import preserves the project's existing
  invariant that every files.file_key is prefixed with its row's user_id;
  stats / purge / delete / download routes work unchanged. URL-encodes the
  copy source so titles with spaces or '&' don't break the copy.
- Universal 7-day expiry cap, no tier differentiation, no "never". DMCA-risk
  reduction. Picker defaults to 3 days.
- Position-aware shares: "Share current page" toggle (off by default for
  privacy) attaches the sharer's CFI; recipient lands at the same paragraph.
- Per-user 50-share cap, rate limiting via Cache-Control: no-store on
  token-bearing responses, atomic SQL increment for download_count via a
  SECURITY DEFINER function so the public confirm beacon stays safe under
  concurrent fire.
- Soft revocation: presigned download URLs (5-min TTL) cannot be cancelled
  before TTL; documented as accepted v1 behavior.
- token + token_hash hybrid storage: public endpoints look up by hash and
  never select the raw token, so accidental SELECT-* leakage on a public
  route can't expose the bearer credential.
- Mobile / desktop Tauri share via tauri-plugin-sharekit; web falls back to
  navigator.share with a clipboard fallback when no native share method
  exists. Share-sheet dismissal no longer silently copies.

UI:
- New Dialog with a settings-card group: iOS-style segmented duration picker
  + toggle slider for "Share current page", on a single row each.
- Reader top-bar Share button, library context-menu Share entry, manage-
  shares list with cover thumbnails and overflow menu.
- New <SegmentedControl> primitive in src/components for reuse.

Coverage:
- Unit tests for token utils + URL parser (20 new tests, full suite at 3445).
- 31 locales translated for all new strings; en plurals hand-added per the
  project's hand-curated en convention.

DB migration in docker/volumes/db/migrations/002_add_book_shares.sql adds
the book_shares table, RLS policies, and the increment_book_share_download
RPC. Migration is idempotent.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

apps/readest-app/src/utils/object.ts

@@ -43,3 +43,39 @@ export const deleteObject = async (fileKey: string, bucketName?: string) => {
     return await s3Storage.deleteObject(bucketName, fileKey);
   }
 };
+
+// Returns true if the object exists in storage. Used to verify uploads completed
+// before treating a `files` row as shareable.
+export const objectExists = async (fileKey: string, bucketName?: string): Promise<boolean> => {
+  const storageType = getStorageType();
+  try {
+    if (storageType === 'r2') {
+      bucketName = bucketName || process.env['R2_BUCKET_NAME'] || '';
+      const response = await r2Storage.headObject(bucketName, fileKey);
+      return response.ok;
+    } else {
+      bucketName = bucketName || process.env['S3_BUCKET_NAME'] || '';
+      await s3Storage.headObject(bucketName, fileKey);
+      return true;
+    }
+  } catch {
+    return false;
+  }
+};
+
+// Server-side byte copy used by /api/share/[token]/import to clone a shared
+// book into the recipient's namespace without egress.
+export const copyObject = async (
+  sourceFileKey: string,
+  destFileKey: string,
+  bucketName?: string,
+) => {
+  const storageType = getStorageType();
+  if (storageType === 'r2') {
+    bucketName = bucketName || process.env['R2_BUCKET_NAME'] || '';
+    return await r2Storage.copyObject(bucketName, sourceFileKey, destFileKey);
+  } else {
+    bucketName = bucketName || process.env['S3_BUCKET_NAME'] || '';
+    return await s3Storage.copyObject(bucketName, sourceFileKey, destFileKey);
+  }
+};