MusicBrainz: Add project URL to User-Agent per API requirements

MusicBrainz mandates a meaningful User-Agent with contact info, warning
that bare strings can trigger IP blocking under load. Our client was
sending `SoulSync/2.3` with no contact — and the search adapter passed
an app version hard-coded at "2.3" that's now stale (UI is at 2.40).

Fix: default contact to the project URL (`https://github.com/Nezreka/SoulSync`)
when no email is supplied, so every request lands as
`SoulSync/<version> ( https://github.com/Nezreka/SoulSync )`. Drop the
search-adapter version suffix to a generic "2" since the exact UI minor
version would add noise to every MB request without helping operators
track issues.

Reference: https://musicbrainz.org/doc/MusicBrainz_API — "it is
important that your application sets a proper User-Agent string."

core/musicbrainz_client.py

@@ -44,28 +44,31 @@ def rate_limited(func):
 
 class MusicBrainzClient:
     """Client for interacting with MusicBrainz API"""
-    
+
     BASE_URL = "https://musicbrainz.org/ws/2"
-    
+    # MusicBrainz mandates a meaningful User-Agent with contact info. Falling back
+    # to a bare name/version risks IP blocking under load — include the project
+    # URL so MB operators have a way to reach us if we misbehave.
+    DEFAULT_CONTACT = "https://github.com/Nezreka/SoulSync"
+
     def __init__(self, app_name: str = "SoulSync", app_version: str = "1.0", contact_email: str = ""):
         """
         Initialize MusicBrainz client
-        
+
         Args:
             app_name: Name of the application
             app_version: Version of the application
-            contact_email: Contact email (optional but recommended)
+            contact_email: Contact email or URL (defaults to project URL when empty)
         """
-        self.user_agent = f"{app_name}/{app_version}"
-        if contact_email:
-            self.user_agent += f" ( {contact_email} )"
-        
+        contact = contact_email or self.DEFAULT_CONTACT
+        self.user_agent = f"{app_name}/{app_version} ( {contact} )"
+
         self.session = requests.Session()
         self.session.headers.update({
             'User-Agent': self.user_agent,
             'Accept': 'application/json'
         })
-        
+
         logger.info(f"MusicBrainz client initialized with user agent: {self.user_agent}")
     
     @rate_limited

core/musicbrainz_search.py

@@ -116,7 +116,10 @@ class MusicBrainzSearchClient:
 
     def __init__(self):
         from core.musicbrainz_client import MusicBrainzClient
-        self._client = MusicBrainzClient("SoulSync", "2.3")
+        # Client defaults to the project URL as its User-Agent contact,
+        # which is what MusicBrainz wants. Version stays generic ("2") —
+        # the exact UI minor version would add noise to every request.
+        self._client = MusicBrainzClient("SoulSync", "2")
         self._art_cache: Dict[str, Optional[str]] = {}  # mbid -> url
 
     def _cached_art(self, release_mbid: str, release_group_mbid: str = '') -> Optional[str]: