feat: add insta snapshot testing for TUI components

- Add insta dev-dependency for visual regression testing
- Create lib.rs to expose modules for integration tests
- Add snapshot tests for progress_bar, topbar, library, help modal
- Add unit tests for LibraryState navigation
- Move all tests to tests/ directory (proper Rust convention)
- Make build.rs skip proto compilation when protoc unavailable
- Add docs/testing-possible-solutions.md with testing strategies

src/grpc/mod.rs

@@ -17,7 +17,10 @@ pub enum GrpcRequest {
 #[allow(dead_code, clippy::large_enum_variant)]
 pub enum GrpcResponse {
     Artists(Vec<ArtistSummary>),
-    Album { album: AlbumDetail, tracks: Vec<TrackDetail> },
+    Album {
+        album: AlbumDetail,
+        tracks: Vec<TrackDetail>,
+    },
     Error(String),
 }
 
@@ -46,14 +49,11 @@ impl GrpcClient {
         &mut self,
         album_id: String,
     ) -> Result<(AlbumDetail, Vec<TrackDetail>), tonic::Status> {
-        let response = self
-            .music
-            .get_album(GetAlbumRequest { album_id })
-            .await?;
+        let response = self.music.get_album(GetAlbumRequest { album_id }).await?;
         let inner = response.into_inner();
-        let album = inner.album.ok_or_else(|| {
-            tonic::Status::not_found("Album not found in response")
-        })?;
+        let album = inner
+            .album
+            .ok_or_else(|| tonic::Status::not_found("Album not found in response"))?;
         Ok((album, inner.tracks))
     }
 }
@@ -84,7 +84,7 @@ pub fn spawn_grpc_worker(
                 GrpcRequest::GetAlbum { album_id } => match client.get_album(album_id).await {
                     Ok((album, tracks)) => GrpcResponse::Album { album, tracks },
                     Err(e) => GrpcResponse::Error(e.to_string()),
-                }
+                },
             };
 
             if resp_tx.send(response).await.is_err() {