feat: migrate browser automation from Playwright MCP to CLI, fix headless setting

Major changes across 21 files (755 additions, 196 deletions):

Browser Automation Migration:
- Add versioned project migration system (prompts.py) with content-based
  detection and section-level regex replacement for coding/testing prompts
- Migrate STEP 5 (browser verification) and BROWSER AUTOMATION sections
  in coding prompt template to use playwright-cli commands
- Migrate STEP 2 and AVAILABLE TOOLS sections in testing prompt template
- Migration auto-runs at agent startup (autonomous_agent_demo.py), copies
  playwright-cli skill, scaffolds .playwright/cli.config.json, updates
  .gitignore, and stamps .migration_version file
- Add playwright-cli command validation to security allowlist (security.py)
  with tests for allowed subcommands and blocked eval/run-code

Headless Browser Setting Fix:
- Add _apply_playwright_headless() to process_manager.py that reads/updates
  .playwright/cli.config.json before agent subprocess launch
- Remove dead PLAYWRIGHT_HEADLESS env var that was never consumed
- Settings UI toggle now correctly controls visible browser window

Playwright CLI Auto-Install:
- Add ensurePlaywrightCli() to lib/cli.js for npm global entry point
- Add playwright-cli detection + npm install to start.bat, start.sh,
  start_ui.bat, start_ui.sh for all startup paths

Other Improvements:
- Add project folder path tooltip to ProjectSelector.tsx dropdown items
- Remove legacy Playwright MCP server configuration from client.py
- Update CLAUDE.md with playwright-cli skill documentation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ui/src/components/ProjectSelector.tsx

@@ -75,6 +75,7 @@ export function ProjectSelector({
             variant="outline"
             className="min-w-[140px] sm:min-w-[200px] justify-between"
             disabled={isLoading}
+            title={selectedProjectData?.path}
           >
             {isLoading ? (
               <Loader2 size={18} className="animate-spin" />
@@ -101,6 +102,7 @@ export function ProjectSelector({
               {projects.map(project => (
                 <DropdownMenuItem
                   key={project.name}
+                  title={project.path}
                   className={`flex items-center justify-between cursor-pointer ${
                     project.name === selectedProject ? 'bg-primary/10' : ''
                   }`}