Clean up dead Go code in handlers, pages, and stores

- Remove "chat" from surface disable guard (only admin needs it)
- Remove "chat" from IsSurfaceEnabled always-on check
- Remove unused fmt.Sprintf references in team stores
- Update stale comments referencing personas and chat surfaces

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/store/sqlite/team.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"database/sql"
 	"encoding/json"
-	"fmt"
 	"time"
 
 	"switchboard-core/models"
@@ -231,8 +230,6 @@ func (s *TeamStore) IsMember(ctx context.Context, teamID, userID string) (bool,
 	return exists, err
 }
 
-// unused but keeping for reference
-var _ = fmt.Sprintf
 
 // ── CS1 additions (v0.29.0) ─────────────────────────────────────────────