The store's layout names live in the core: local::DB_FILE, BLOBS_DIR

"inkwell.db" and "blobs" were spelled out in the ffi and the desktop (whose copy
of DB_FILE sat in the crossover shim). The layout is the core's, the same on
every client, so the names are now core constants and both clients read them.

DRY pass #2, batch 1, F4 (#5372).

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

android/ffi/src/lib.rs

@@ -163,10 +163,10 @@ impl Inkwell {
         let dir = PathBuf::from(data_dir);
         std::fs::create_dir_all(&dir).map_err(CoreError::store)?;
 
-        let db = local::open(&dir.join("inkwell.db")).map_err(CoreError::store)?;
+        let db = local::open(&dir.join(local::DB_FILE)).map_err(CoreError::store)?;
         log::info!("local store ready — {}", local::summary(&db));
 
-        let blobs = BlobStore::new(dir.join("blobs")).map_err(CoreError::store)?;
+        let blobs = BlobStore::new(dir.join(local::BLOBS_DIR)).map_err(CoreError::store)?;
         Ok(Arc::new(Inkwell {
             db,
             blobs,