all: delete the code nothing calls

From the audit (#5178). Each was unreachable from every client:

- Checklist add-item and delete-item: REST POST /items and DELETE /items/<id>,
  the Tauri commands, the store, rest and local adapters, the core's
  add_item/delete_item, set_item_text and remove_item, and the FFI exports.
  Adding, rewording and removing an item are body edits in every editor. The
  checked toggle stays, and its rewriter is simpler without the drop branch.
- Manual unfurl: POST /unfurl and its adapters. Previews arrive in the
  background after a save (unfurl_queue).
- The /api/config `android_client` key, android_release() and the
  APK_NAME/MANIFEST_NAME aliases. Phones poll /api/client/android.
- users.email_verified and users.avatar_path (migration 0037). Nothing set
  the first or read the second; the SMTP reset never checked verification.
- derive::extract_tags (only tests used it; the shared fixture now runs
  through extract_tag_spans), the unused check and link icons, and the
  unused editor_add_item string.
- The blob scheme is renamed tsblob -> inkblob. URLs are built as notes are
  read, so nothing stored carries the old one.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

android/app/src/main/res/values/strings.xml

@@ -40,7 +40,6 @@
     <string name="editor_back">Back to notes</string>
     <string name="editor_add_checklist">Add a checklist</string>
     <string name="editor_body_hint">Take a note…</string>
-    <string name="editor_add_item">Add item</string>
     <string name="editor_remove_item">Remove item</string>
     <string name="editor_remove_label">Remove tag</string>
     <string name="editor_reminder">Set a reminder</string>