fix: honor library param in /image, /photos, /memories

The Phase 3 plumbing accepted `library=` but didn't actually route
requests through the scoped library once it was resolved. Three
concrete bugs surfaced when testing against a second mounted library:

- `/image` always resolved paths against AppState.base_path (primary),
  so thumbnails for non-primary libraries 400'd when their rel_paths
  didn't exist under primary. Now resolves against the scoped library
  and defaults to primary when the param is omitted.

- `/memories` walked the scoped library correctly but its helper
  functions hardcoded `library_id: PRIMARY_LIBRARY_ID` on every
  MemoryItem, causing clients to route thumbnails back to primary
  regardless of which library the memory actually came from.

- `/photos` non-recursive listing delegated to a `RealFileSystem`
  constructed from AppState.base_path at startup, so walks always
  hit primary even when `library=2` was passed. The non-primary
  path now uses list_files against the scoped library's root;
  primary still goes through FileSystemAccess to preserve the
  existing test mock plumbing.

Also adds `library` to ThumbnailRequest so the /image query param
is actually parsed.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/main.rs

@@ -104,12 +104,26 @@ async fn get_image(
 
     let mut span = tracer.start_with_context("get_image", &context);
 
-    if let Some(path) = is_valid_full_path(&app_state.base_path, &req.path, false) {
+    // Resolve library from query param; default to primary so clients that
+    // don't yet send `library=` continue to work.
+    let library = match libraries::resolve_library_param(
+        &app_state,
+        req.library.as_deref(),
+    ) {
+        Ok(Some(lib)) => lib,
+        Ok(None) => app_state.primary_library(),
+        Err(msg) => {
+            span.set_status(Status::error(msg.clone()));
+            return HttpResponse::BadRequest().body(msg);
+        }
+    };
+
+    if let Some(path) = is_valid_full_path(&library.root_path, &req.path, false) {
         let image_size = req.size.unwrap_or(PhotoSize::Full);
         if image_size == PhotoSize::Thumb {
             let relative_path = path
-                .strip_prefix(&app_state.base_path)
-                .expect("Error stripping base path prefix from thumbnail");
+                .strip_prefix(&library.root_path)
+                .expect("Error stripping library root prefix from thumbnail");
             let relative_path_str = relative_path.to_string_lossy().replace('\\', "/");
 
             let thumbs = &app_state.thumbnail_path;