feat: Sprint 17 -- workspace breadcrumbs, slash commands, send key setting

Track A: Workspace breadcrumb navigation
- Breadcrumb path bar with clickable segments when inside subdirectories
- Up button in panel header for parent directory navigation
- S.currentDir state tracking; file ops stay in current directory
- New file/folder creation respects current subdirectory

Track B: Slash commands foundation
- New commands.js module (7th JS module) with command registry and parser
- Built-in commands: /help, /clear, /model, /workspace, /new
- Autocomplete dropdown on / input with arrow/tab/enter/escape navigation
- Unrecognized commands pass through to agent normally

Track C: Send key setting (closes #26)
- send_key added to settings defaults in api/config.py
- Settings panel dropdown: Enter (default) vs Ctrl/Cmd+Enter
- Keydown handler rewritten for autocomplete + send key preference
- Setting loaded on boot, persisted to settings.json

5 new tests, 242 total (219 passing, 22 pre-existing failures, 0 regressions).

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

api/config.py

@@ -594,6 +594,7 @@ def _get_session_agent_lock(session_id: str) -> threading.Lock:
 _SETTINGS_DEFAULTS = {
     'default_model': DEFAULT_MODEL,
     'default_workspace': str(DEFAULT_WORKSPACE),
+    'send_key': 'enter',  # 'enter' or 'ctrl+enter'
 }
 
 def load_settings() -> dict:
@@ -609,12 +610,18 @@ def load_settings() -> dict:
     return settings
 
 _SETTINGS_ALLOWED_KEYS = set(_SETTINGS_DEFAULTS.keys())
+_SETTINGS_ENUM_VALUES = {
+    'send_key': {'enter', 'ctrl+enter'},
+}
 
 def save_settings(settings: dict) -> dict:
     """Save settings to disk. Returns the merged settings. Ignores unknown keys."""
     current = load_settings()
     for k, v in settings.items():
         if k in _SETTINGS_ALLOWED_KEYS:
+            # Validate enum-constrained keys
+            if k in _SETTINGS_ENUM_VALUES and v not in _SETTINGS_ENUM_VALUES[k]:
+                continue
             current[k] = v
     SETTINGS_FILE.write_text(
         json.dumps(current, ensure_ascii=False, indent=2),