refactor(toc): cache navigable structure per book (#3869)

* refactor(toc): cache TOC + section fragments per book

Moves the TOC regrouping and section-fragment computation out of
foliate-js/epub.js #updateSubItems into the readest client as
computeBookNav / hydrateBookNav in utils/toc.ts. The result is
persisted to Books/{hash}/nav.json — capturing the book's full
navigable structure (TOC hierarchy + sections with hierarchical
fragments). Compute once, persist locally, hydrate on subsequent
opens. Designed to serve current human-facing navigation (TOC
sidebar, progress math) and future agentic navigation (LLM-driven
seeking by structural location).

Versioned by BOOK_NAV_VERSION for forward invalidation. Existing
books regenerate transparently on next open.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* chore: update worktree scripts

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/readest-app/scripts/worktree-new.ts

@@ -134,22 +134,6 @@ if (/^\d+$/.test(arg)) {
 console.error('\n--- Rebasing onto origin/main ---');
 execSync('git rebase origin/main', { stdio: gitStdio, cwd: worktreePath });
 
-// Symlink shared directories into the new worktree, pointing at the bare repo's
-// git common dir so all worktrees share the same settings without duplication.
-const gitCommonDir = execSync('git rev-parse --git-common-dir', {
-  encoding: 'utf8',
-  cwd: repoRoot,
-}).trim();
-for (const dir of ['.claude', '.local-settings']) {
-  const sharedDir = path.resolve(repoRoot, gitCommonDir, dir);
-  const newDir = path.join(worktreePath, dir);
-  fs.mkdirSync(sharedDir, { recursive: true });
-  if (!fs.existsSync(newDir)) {
-    // 'junction' works without elevated privileges on Windows; ignored on Unix
-    fs.symlinkSync(sharedDir, newDir, 'junction');
-  }
-}
-
 // Repoint submodule URLs to local .git/modules/ clones to avoid remote fetches.
 // Submodules without a local cache fall back to the remote URL.
 console.error('\n--- Initializing submodules (using local objects) ---');
@@ -250,7 +234,7 @@ if (fs.existsSync(androidGenDir)) {
     stdio: gitStdio,
     cwd: dstAppDir,
   });
-  execSync(`git checkout ${appRelPath}/src-tauri/gen/android`, {
+  execSync(`git checkout ${appRelPath}/src-tauri/gen/android ${appRelPath}/src-tauri/icons`, {
     stdio: gitStdio,
     cwd: worktreePath,
   });