feat: Add robust fallback mechanisms for spec creation chat

Add multiple escape hatches to prevent users from getting stuck during
spec creation when the WebSocket completion signal fails.

Changes:
- Add "Exit to Project" button always visible in chat header
- Add /exit command detection to immediately exit to project
- Add backend GET /api/spec/status/{project} endpoint to poll status file
- Add getSpecStatus() API function in frontend
- Add status file polling (every 3s) in useSpecChat hook
- Update create-spec.md with status file write instructions

How it works:
1. Happy path: Claude writes .spec_status.json as final step, UI polls
   and detects completion, shows "Continue to Project" button
2. Escape hatch: User can always click "Exit to Project" or type /exit
   to instantly select the project and close modal, then manually start
   the agent from the main UI

This ensures users always have a way forward even if the WebSocket
completion detection fails due to tool call tracking issues.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

ui/src/components/NewProjectModal.tsx

@@ -148,6 +148,12 @@ export function NewProjectModal({
     setSpecMethod(null)
   }
 
+  const handleExitToProject = () => {
+    // Exit chat and go directly to project - user can start agent manually
+    onProjectCreated(projectName.trim())
+    handleClose()
+  }
+
   const handleClose = () => {
     setStep('name')
     setProjectName('')
@@ -178,6 +184,7 @@ export function NewProjectModal({
           projectName={projectName.trim()}
           onComplete={handleSpecComplete}
           onCancel={handleChatCancel}
+          onExitToProject={handleExitToProject}
           initializerStatus={initializerStatus}
           initializerError={initializerError}
           onRetryInitializer={handleRetryInitializer}