Initial commit — Tauri image gallery with sqlite-vec

Sets up Tauri v2 + React frontend with SQLite metadata store,
sqlite-vec for CLIP embedding infrastructure, and r2d2 connection
pool replacing the single Arc<Mutex<Connection>>. Indexer now uses
rayon for parallel file metadata collection.

src-tauri/src/thumbnail.rs

@@ -0,0 +1,6 @@
+use std::path::Path;
+
+/// Gets image dimensions without fully decoding.
+pub fn get_dimensions(image_path: &Path) -> Option<(u32, u32)> {
+    image::image_dimensions(image_path).ok()
+}