feat(claude): add 'auto' startup permission mode

Adds Anthropic's classifier-guarded low-prompt mode (--permission-mode
auto) as a fourth ClaudeMode alongside skip-permissions/normal/allowedTools.
Wired through both spawn paths (buildPermissionArgs for direct PTY,
buildClaudePermissionFlags for tmux), the getClaudeModeConfig validator,
and the App Settings Startup Mode picker. Exports buildSpawnCommand for
test coverage.

This is the prerequisite for multi-user mode section 6.3, which downgrades
non-granted users' sessions to 'auto'.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/session.ts

@@ -1523,7 +1523,7 @@ export class Session extends EventEmitter {
 
       // === Auto-accept workspace trust dialog ===
       // Claude CLI 2.x shows "Yes, I trust this folder" prompt on first launch per directory.
-      // Codeman sessions always use --dangerously-skip-permissions, so auto-accept.
+      // Codeman sessions run permission-skipping or classifier-guarded (auto) modes, so auto-accept.
       if (!this._trustDialogAccepted && data.includes('trust this folder')) {
         this._trustDialogAccepted = true;
         console.log(`[Session] Auto-accepting workspace trust dialog for: ${this.id}`);