perf(suggestions): add skip_vector_build option for faster initial load

- Add skip_vector_build config option to SuggestionConfig
- When true, skips ensure_vector calls (which can be very slow)
- Uses only cached/existing vectors for similarity search
- Frontend now uses skip_vector_build=true for initial load

- Add timestamped logging helper in frontend component

src/lib/components/PlaylistSuggestions.svelte

@@ -57,6 +57,12 @@
   // Track the last playlist we loaded for
   let lastLoadedPlaylistId = $state<number | null>(null);
 
+  // Helper for timestamped logs
+  function log(...args: unknown[]) {
+    const ts = new Date().toISOString().slice(11, 23);
+    console.log(`[${ts}] [Suggestions]`, ...args);
+  }
+
   // Load suggestions when playlist/artists change
   $effect(() => {
     const artistCount = artists.length;
@@ -64,7 +70,7 @@
 
     // Only load if we have artists and haven't loaded for this playlist yet
     if (artistCount > 0 && currentPlaylistId !== lastLoadedPlaylistId && !loading) {
-      console.log('[Suggestions] Effect triggered, playlist:', currentPlaylistId, 'artists:', artistCount);
+      log('Effect triggered, playlist:', currentPlaylistId, 'artists:', artistCount);
       lastLoadedPlaylistId = currentPlaylistId;
       hasLoadedOnce = false;
       pool = [];
@@ -74,27 +80,27 @@
 
   async function loadSuggestions(expanded: boolean) {
     if (loading) {
-      console.log('[Suggestions] Already loading, skipping');
+      log('Already loading, skipping');
       return;
     }
 
     const poolSize = expanded ? EXPANDED_POOL : INITIAL_POOL;
-    console.log(`[Suggestions] Starting load (expanded=${expanded}, poolSize=${poolSize}, artists=${artists.length})`);
+    log(`Starting load (expanded=${expanded}, poolSize=${poolSize}, artists=${artists.length})`);
     const startTime = performance.now();
 
     loading = true;
     error = null;
 
     try {
-      console.log('[Suggestions] Calling backend...');
+      log('Calling backend...');
       result = await getPlaylistSuggestionsV2(
         artists,
         excludeTrackIds,
         showReasons,
-        { max_pool_size: poolSize }
+        { max_pool_size: poolSize, skip_vector_build: true }
       );
       const elapsed = ((performance.now() - startTime) / 1000).toFixed(2);
-      console.log(`[Suggestions] Backend returned in ${elapsed}s:`, {
+      log(`Backend returned in ${elapsed}s:`, {
         tracks: result.tracks.length,
         sourceArtists: result.source_artists.length,
         playlistArtists: result.playlist_artists_count,
@@ -105,7 +111,7 @@
       hasLoadedOnce = true;
     } catch (err) {
       const elapsed = ((performance.now() - startTime) / 1000).toFixed(2);
-      console.error(`[Suggestions] Failed after ${elapsed}s:`, err);
+      log(`Failed after ${elapsed}s:`, err);
       error = err instanceof Error ? err.message : 'Failed to load suggestions';
       pool = [];
     } finally {

src/lib/services/playlistSuggestionsService.ts

@@ -15,6 +15,8 @@ export interface SuggestionConfig {
   max_pool_size?: number;
   vector_max_age_days?: number;
   min_similarity?: number;
+  /** Skip building vectors - only use existing cached vectors (faster but may have fewer results) */
+  skip_vector_build?: boolean;
 }
 
 export interface SuggestedTrack {