feat: Add YOLO mode for rapid prototyping without browser testing

Add a new YOLO (You Only Live Once) mode that skips all browser testing
and regression tests for faster feature iteration during prototyping.

Changes made:

**Core YOLO Mode Implementation:**
- Add --yolo CLI flag to autonomous_agent_demo.py
- Update agent.py to accept yolo_mode parameter and select appropriate prompt
- Modify client.py to conditionally include Playwright MCP server (excluded in YOLO mode)
- Add coding_prompt_yolo.template.md with static analysis only verification
- Add get_coding_prompt_yolo() to prompts.py

**Server/API Updates:**
- Add AgentStartRequest schema with yolo_mode field
- Update AgentStatus to include yolo_mode
- Modify process_manager.py to pass --yolo flag to subprocess
- Update agent router to accept yolo_mode in start request

**UI Updates:**
- Add YOLO toggle button (lightning bolt icon) in AgentControl
- Show YOLO mode indicator when agent is running in YOLO mode
- Add useAgentStatus hook to track current mode
- Update startAgent API to accept yoloMode parameter
- Add YOLO toggle in SpecCreationChat completion flow

**Spec Creation Improvements:**
- Fix create-spec.md to properly replace [FEATURE_COUNT] placeholder
- Add REQUIRED FEATURE COUNT section to initializer_prompt.template.md
- Fix spec_chat_session.py to create security settings file for Claude SDK
- Delete app_spec.txt before spec creation to allow fresh creation

**Documentation:**
- Add YOLO mode section to CLAUDE.md with usage examples
- Add checkpoint.md slash command for creating detailed commits

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

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

server/services/spec_chat_session.py

@@ -7,6 +7,7 @@ Uses the create-spec.md skill to guide users through app spec creation.
 """
 
 import asyncio
+import json
 import logging
 import shutil
 import threading
@@ -87,6 +88,33 @@ class SpecChatSession:
         # Ensure project directory exists (like CLI does in start.py)
         self.project_dir.mkdir(parents=True, exist_ok=True)
 
+        # Delete app_spec.txt so Claude can create it fresh
+        # The SDK requires reading existing files before writing, but app_spec.txt is created new
+        # Note: We keep initializer_prompt.md so Claude can read and update the template
+        prompts_dir = self.project_dir / "prompts"
+        app_spec_path = prompts_dir / "app_spec.txt"
+        if app_spec_path.exists():
+            app_spec_path.unlink()
+            logger.info("Deleted scaffolded app_spec.txt for fresh spec creation")
+
+        # Create security settings file (like client.py does)
+        # This grants permissions for file operations in the project directory
+        security_settings = {
+            "sandbox": {"enabled": False},  # Disable sandbox for spec creation
+            "permissions": {
+                "defaultMode": "acceptEdits",
+                "allow": [
+                    "Read(./**)",
+                    "Write(./**)",
+                    "Edit(./**)",
+                    "Glob(./**)",
+                ],
+            },
+        }
+        settings_file = self.project_dir / ".claude_settings.json"
+        with open(settings_file, "w") as f:
+            json.dump(security_settings, f, indent=2)
+
         # Replace $ARGUMENTS with absolute project path (like CLI does in start.py:184)
         # Using absolute path avoids confusion when project folder name differs from app name
         project_path = str(self.project_dir.resolve())
@@ -111,6 +139,7 @@ class SpecChatSession:
                     permission_mode="acceptEdits",  # Auto-approve file writes for spec creation
                     max_turns=100,
                     cwd=str(self.project_dir.resolve()),
+                    settings=str(settings_file.resolve()),
                 )
             )
             # Enter the async context and track it