fix(evolution): use CompareAndSwap for atomic lockStoreFile repair

Replace the Delete+LoadOrStore pattern with CompareAndSwap to
atomically swap in a fresh mutex when a corrupted entry is detected.

Changes:
- Use a retry loop with CAS instead of Delete+LoadOrStore, avoiding
  the race where two goroutines could create different mutexes
- Add nil check: a nil *sync.Mutex passes the type assertion but
  panics on Lock() — now handled by the CAS recovery path
- Use continue-loop retry instead of unchecked second assertion

CompareAndSwap guarantees that when multiple goroutines detect a
corrupted entry, they converge on the same replacement mutex.

pkg/evolution/store.go

@@ -554,19 +554,20 @@ func isInvalidJSON(err error) bool {
 }
 
 func lockStoreFile(path string) func() {
-	actual, _ := storeFileLocks.LoadOrStore(path, &sync.Mutex{})
-	mu, ok := actual.(*sync.Mutex)
-	if !ok {
-		// Delete the corrupted entry so that the next LoadOrStore
-		// atomically creates a fresh mutex. Multiple goroutines may
-		// race to Delete, but LoadOrStore ensures they all converge
-		// on the same mutex before entering the critical section.
-		storeFileLocks.Delete(path)
-		actual, _ = storeFileLocks.LoadOrStore(path, &sync.Mutex{})
-		mu = actual.(*sync.Mutex)
+	for {
+		actual, _ := storeFileLocks.LoadOrStore(path, &sync.Mutex{})
+		mu, ok := actual.(*sync.Mutex)
+		if !ok || mu == nil {
+			// Corrupted entry (wrong type or nil *sync.Mutex).
+			// Atomically swap in a fresh mutex via CompareAndSwap.
+			// If CAS fails, another goroutine already replaced it —
+			// just retry the loop to pick up the valid entry.
+			storeFileLocks.CompareAndSwap(path, actual, &sync.Mutex{})
+			continue
+		}
+		mu.Lock()
+		return mu.Unlock
 	}
-	mu.Lock()
-	return mu.Unlock
 }
 
 func (s *Store) profilePath(workspaceID, skillName string) (string, error) {