feat: implement gallery feed with social features and SSE

- Cursor-based feed endpoint using v_feed view with hashtag filtering
- Like toggle (INSERT ON CONFLICT), comments CRUD
- Feed delta endpoint for SSE-driven incremental updates
- SSE client with Page Visibility API (pause/reconnect)
- Responsive photo/video grid with infinite scroll
- Hashtag filter chips, lightbox modal with comments
- Media file serving via tower-http ServeDir

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/main.rs

@@ -1,6 +1,7 @@
 use anyhow::Result;
 use axum::routing::{delete, get, patch, post};
 use axum::Router;
+use tower_http::services::ServeDir;
 use tracing_subscriber::{layer::SubscriberExt, util::SubscriberInitExt};
 
 mod auth;
@@ -45,12 +46,27 @@ async fn main() -> Result<()> {
             "/api/v1/upload/{id}",
             patch(handlers::upload::edit_upload).delete(handlers::upload::delete_upload),
         )
+        // Feed
+        .route("/api/v1/feed", get(handlers::feed::feed))
+        .route("/api/v1/feed/delta", get(handlers::feed::feed_delta))
+        .route("/api/v1/hashtags", get(handlers::feed::hashtags))
+        // Social
+        .route("/api/v1/upload/{id}/like", post(handlers::social::toggle_like))
+        .route(
+            "/api/v1/upload/{id}/comments",
+            get(handlers::social::list_comments).post(handlers::social::add_comment),
+        )
+        .route("/api/v1/comment/{id}", delete(handlers::social::delete_comment))
         // SSE
         .route("/api/v1/stream", get(handlers::sse::stream));
 
+    // Serve media files from disk
+    let media_service = ServeDir::new(&config.media_path);
+
     let router = Router::new()
         .route("/health", get(|| async { "ok" }))
         .merge(api)
+        .nest_service("/media", media_service)
         .with_state(state);
 
     let listener = tokio::net::TcpListener::bind(("0.0.0.0", config.app_port)).await?;