fix: add title validation — sanitize, length limit, control char stripping

- Add SessionDB.sanitize_title() static method:
  - Strips ASCII control chars (null, bell, ESC, etc.) except whitespace
  - Strips problematic Unicode controls (zero-width, RTL override, BOM)
  - Collapses whitespace runs, strips edges
  - Normalizes empty/whitespace-only to None
  - Enforces 100 char max length (raises ValueError)
- set_session_title() now calls sanitize_title() internally,
  so all call sites (CLI, gateway, auto-lineage) are protected
- CLI /title handler sanitizes early to show correct feedback
- Gateway /title handler sanitizes early to show correct feedback
- 24 new tests: sanitize_title (17 cases covering control chars,
  zero-width, RTL, BOM, emoji, CJK, length, integration),
  gateway validation (too long, control chars, only-control-chars)

cli.py

@@ -2116,12 +2116,20 @@ class HermesCLI:
         elif cmd_lower.startswith("/title"):
             parts = cmd_original.split(maxsplit=1)
             if len(parts) > 1:
-                new_title = parts[1].strip()
-                if new_title:
+                raw_title = parts[1].strip()
+                if raw_title:
                     if self._session_db:
-                        # Check if session exists in DB yet
-                        session = self._session_db.get_session(self.session_id)
-                        if session:
+                        # Sanitize the title early so feedback matches what gets stored
+                        try:
+                            from hermes_state import SessionDB
+                            new_title = SessionDB.sanitize_title(raw_title)
+                        except ValueError as e:
+                            _cprint(f"  {e}")
+                            new_title = None
+                        if not new_title:
+                            _cprint("  Title is empty after cleanup. Please use printable characters.")
+                        elif self._session_db.get_session(self.session_id):
+                            # Session exists in DB — set title directly
                             try:
                                 if self._session_db.set_session_title(self.session_id, new_title):
                                     _cprint(f"  Session title set: {new_title}")
@@ -2131,7 +2139,7 @@ class HermesCLI:
                                 _cprint(f"  {e}")
                         else:
                             # Session not created yet — defer the title
-                            # Check uniqueness proactively
+                            # Check uniqueness proactively with the sanitized title
                             existing = self._session_db.get_session_by_title(new_title)
                             if existing:
                                 _cprint(f"  Title '{new_title}' is already in use by session {existing['id']}")