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>

desktop/src-tauri/src/lib.rs

@@ -126,7 +126,7 @@ pub fn run() {
                 log_crossover(&legacy, crossover::adopt_legacy_data(&legacy, &dir));
             }
             std::fs::create_dir_all(&dir)?;
-            let db_path = dir.join(crossover::DB_FILE);
+            let db_path = dir.join(local::DB_FILE);
             log::info!("opening local store: {}", db_path.display());
             let db = local::open(&db_path)?;
             log::info!("local store ready — {}", local::summary(&db));
@@ -142,7 +142,7 @@ pub fn run() {
             app.manage(db);
             // Attachment bytes live beside the database, filed by content hash, so a
             // synced image is readable with no network (M10.7d).
-            let blobs = sync::blobs::BlobStore::new(dir.join("blobs"))?;
+            let blobs = sync::blobs::BlobStore::new(dir.join(local::BLOBS_DIR))?;
             log::info!("attachment store ready: {}", blobs.root().display());
             // Hand the directory to the URI-scheme handler registered below, which
             // was built before this path could be resolved.