Fix Navidrome playlist sync truncation, clarify discovery label

Navidrome fix:
- createPlaylist and other write operations now use POST instead of
  GET. Large playlists (161+ tracks) exceeded URL length limits when
  all songId params were in the query string, causing silent truncation
  (e.g., only 6 of 161 tracks added). POST sends params as form body
  with no size limit.
- Write operation timeout bumped to 30s (was 10s)
- _WRITE_ENDPOINTS set defines which Subsonic endpoints use POST

UX fix:
- Mirrored playlist cards now show "161/161 discovered on Spotify"
  instead of just "161/161 discovered" — clarifies that discovery
  means metadata matching, not library ownership

core/navidrome_client.py

@@ -301,8 +301,19 @@ class NavidromeClient:
             'f': 'json'  # Response format
         }
 
+    # Subsonic endpoints that modify data — use POST to avoid URL length limits
+    _WRITE_ENDPOINTS = frozenset({
+        'createPlaylist', 'updatePlaylist', 'deletePlaylist',
+        'star', 'unstar', 'scrobble', 'setRating',
+        'createShare', 'updateShare', 'deleteShare',
+        'createUser', 'updateUser', 'deleteUser',
+        'createBookmark', 'deleteBookmark',
+        'startScan',
+    })
+
     def _make_request(self, endpoint: str, params: Optional[Dict[str, Any]] = None) -> Optional[Dict[str, Any]]:
-        """Make authenticated request to Navidrome Subsonic API"""
+        """Make authenticated request to Navidrome Subsonic API.
+        Uses POST for write operations (avoids URL length limits with large playlists)."""
         if not self.base_url or not self.username:
             return None
 
@@ -314,7 +325,12 @@ class NavidromeClient:
             auth_params.update(params)
 
         try:
-            response = requests.get(url, params=auth_params, timeout=10)
+            # Use POST for write operations to avoid URL length limits
+            # (e.g., createPlaylist with 161 songId params would exceed GET URL limits)
+            if endpoint in self._WRITE_ENDPOINTS:
+                response = requests.post(url, data=auth_params, timeout=30)
+            else:
+                response = requests.get(url, params=auth_params, timeout=10)
             response.raise_for_status()
 
             data = response.json()

webui/static/script.js

@@ -57586,7 +57586,8 @@ function renderMirroredCard(p, container) {
     let ratioHtml = '';
     if (disc > 0) {
         const complete = disc >= tot;
-        ratioHtml = `<span class="discovery-ratio${complete ? ' complete' : ''}">${disc}/${tot} discovered</span>`;
+        const srcName = typeof currentMusicSourceName !== 'undefined' ? currentMusicSourceName : 'metadata';
+        ratioHtml = `<span class="discovery-ratio${complete ? ' complete' : ''}">${disc}/${tot} discovered on ${srcName}</span>`;
     }
 
     const card = document.createElement('div');