fix(review-2): critical — repair comment posting + close export data leak

CR1: the lightbox comment button POSTed to /upload/{id}/comment (singular);
     no such route exists, so every UI-submitted comment 404'd and was lost.
     Fixed to /comments (plural). The prior e2e passed because its seed helper
     POSTs the API directly — added comment-ui.spec.ts which drives the real
     component so this can't regress silently again.

CR2: export archives (Gallery.zip / Memories.zip / HTML viewer) were written
     under media_path, which is a public ServeDir — so GET /media/exports/
     Gallery.zip served the entire event (every photo, caption, comment,
     uploader name) to any anonymous visitor at a guessable URL, bypassing the
     ticket + release gate. Moved exports to a separate EXPORT_PATH (=/exports)
     on its own volume (Dockerfile chown, compose volume, gated handler reads
     the new path). export-leak.spec.ts asserts /media/exports/Gallery.zip → 404.

Riders (git can't split hunks): LightboxModal also gains H3 live-eviction on
comment-deleted/upload-deleted; config.rs also wires compression_concurrency
from boot config (medium).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/src/config.rs

@@ -56,7 +56,13 @@ pub struct AppConfig {
     pub event_name: String,
     pub event_slug: String,
     pub media_path: PathBuf,
+    /// Where export archives are written. MUST be outside `media_path` — that
+    /// directory is served by a public `ServeDir`, so a predictable archive name
+    /// under it would leak the whole gallery to anonymous visitors.
+    pub export_path: PathBuf,
     pub app_port: u16,
+    /// Number of concurrent media compression workers (read once at boot).
+    pub compression_concurrency: usize,
 }
 
 impl AppConfig {
@@ -86,10 +92,18 @@ impl AppConfig {
             media_path: PathBuf::from(
                 std::env::var("MEDIA_PATH").unwrap_or_else(|_| "/media".to_string()),
             ),
+            export_path: PathBuf::from(
+                std::env::var("EXPORT_PATH").unwrap_or_else(|_| "/exports".to_string()),
+            ),
             app_port: std::env::var("APP_PORT")
                 .unwrap_or_else(|_| "3000".to_string())
                 .parse()
                 .context("APP_PORT must be a number")?,
+            compression_concurrency: std::env::var("COMPRESSION_WORKER_CONCURRENCY")
+                .ok()
+                .and_then(|v| v.parse().ok())
+                .filter(|&n| n >= 1)
+                .unwrap_or(2),
         })
     }
 }

backend/src/services/export.rs

@@ -87,15 +87,17 @@ pub fn spawn_export_jobs(
     event_name: String,
     pool: PgPool,
     media_path: PathBuf,
+    export_path: PathBuf,
     sse_tx: broadcast::Sender<SseEvent>,
 ) {
     let pool2 = pool.clone();
     let media_path2 = media_path.clone();
+    let export_path2 = export_path.clone();
     let sse_tx2 = sse_tx.clone();
     let event_name2 = event_name.clone();
 
     tokio::spawn(async move {
-        if let Err(e) = run_zip_export(event_id, &pool, &media_path, &sse_tx).await {
+        if let Err(e) = run_zip_export(event_id, &pool, &media_path, &export_path, &sse_tx).await {
             tracing::error!("ZIP export failed for event {event_id}: {e:#}");
             mark_failed(&pool, event_id, "zip", &e.to_string()).await;
         }
@@ -104,7 +106,7 @@ pub fn spawn_export_jobs(
 
     tokio::spawn(async move {
         if let Err(e) =
-            run_html_export(event_id, &event_name2, &pool2, &media_path2, &sse_tx2).await
+            run_html_export(event_id, &event_name2, &pool2, &media_path2, &export_path2, &sse_tx2).await
         {
             tracing::error!("HTML export failed for event {event_id}: {e:#}");
             mark_failed(&pool2, event_id, "html", &e.to_string()).await;
@@ -119,6 +121,7 @@ async fn run_zip_export(
     event_id: Uuid,
     pool: &PgPool,
     media_path: &Path,
+    export_path: &Path,
     sse_tx: &broadcast::Sender<SseEvent>,
 ) -> Result<()> {
     mark_running(pool, event_id, "zip").await;
@@ -126,7 +129,8 @@ async fn run_zip_export(
     let uploads = query_uploads(pool, event_id).await?;
     let total = uploads.len().max(1) as f32;
 
-    let exports_dir = media_path.join("exports");
+    // Written OUTSIDE media_path: the public /media ServeDir must never reach these.
+    let exports_dir = export_path.to_path_buf();
     tokio::fs::create_dir_all(&exports_dir).await?;
 
     let tmp_path = exports_dir.join("Gallery.zip.tmp");
@@ -193,6 +197,7 @@ async fn run_html_export(
     event_name: &str,
     pool: &PgPool,
     media_path: &Path,
+    export_path: &Path,
     sse_tx: &broadcast::Sender<SseEvent>,
 ) -> Result<()> {
     mark_running(pool, event_id, "html").await;
@@ -205,7 +210,8 @@ async fn run_html_export(
 
     update_progress(pool, event_id, "html", 5).await;
 
-    let exports_dir = media_path.join("exports");
+    // Written OUTSIDE media_path: the public /media ServeDir must never reach these.
+    let exports_dir = export_path.to_path_buf();
     tokio::fs::create_dir_all(&exports_dir).await?;
 
     // 2. Create temp directory for media processing