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>

static/panels.js

@@ -646,6 +646,9 @@ async function loadSettingsPanel(){
       }catch(e){}
       wsSel.value=settings.default_workspace||'';
     }
+    // Send key preference
+    const sendKeySel=$('settingsSendKey');
+    if(sendKeySel) sendKeySel.value=settings.send_key||'enter';
   }catch(e){
     showToast('Failed to load settings: '+e.message);
   }
@@ -654,11 +657,14 @@ async function loadSettingsPanel(){
 async function saveSettings(){
   const model=($('settingsModel')||{}).value;
   const workspace=($('settingsWorkspace')||{}).value;
+  const sendKey=($('settingsSendKey')||{}).value;
   const body={};
   if(model) body.default_model=model;
   if(workspace) body.default_workspace=workspace;
+  if(sendKey) body.send_key=sendKey;
   try{
     await api('/api/settings',{method:'POST',body:JSON.stringify(body)});
+    window._sendKey=sendKey||'enter';
     showToast('Settings saved');
     toggleSettings();
   }catch(e){