fix(auth): ensure JWT sub claim is RFC 7519 compliant string

- Change TokenPayload.sub type from int to str per JWT RFC 7519
- Add user_id property to TokenPayload for int conversion
- Update token creation to serialize user_id as string
- Update token consumers to use payload.user_id
- Change dashboard port from 3000 to 8080
- Add pydantic[email] for email validation
- Update default admin email to admin@sparc.dev

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

SPARC/api.py

@@ -236,7 +236,7 @@ async def refresh_token(request: RefreshRequest):
         )
 
     db = get_db_client()
-    user = db.get_user_by_id(payload.sub)
+    user = db.get_user_by_id(payload.user_id)
 
     if not user:
         raise HTTPException(