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>

lib/cli.js

@@ -517,6 +517,41 @@ function killProcess(pid) {
   }
 }
 
+// ---------------------------------------------------------------------------
+// Playwright CLI
+// ---------------------------------------------------------------------------
+
+/**
+ * Ensure playwright-cli is available globally for browser automation.
+ * Returns true if available (already installed or freshly installed).
+ *
+ * @param {boolean} showProgress - If true, print install progress
+ */
+function ensurePlaywrightCli(showProgress) {
+  try {
+    execSync('playwright-cli --version', {
+      timeout: 10_000,
+      stdio: ['pipe', 'pipe', 'pipe'],
+    });
+    return true;
+  } catch {
+    // Not installed — try to install
+  }
+
+  if (showProgress) {
+    log('      Installing playwright-cli for browser automation...');
+  }
+  try {
+    execSync('npm install -g @playwright/cli', {
+      timeout: 120_000,
+      stdio: ['pipe', 'pipe', 'pipe'],
+    });
+    return true;
+  } catch {
+    return false;
+  }
+}
+
 // ---------------------------------------------------------------------------
 // CLI commands
 // ---------------------------------------------------------------------------
@@ -613,6 +648,14 @@ function startServer(opts) {
   }
   const wasAlreadyReady = ensureVenv(python, repair);
 
+  // Ensure playwright-cli for browser automation (quick check, installs once)
+  if (!ensurePlaywrightCli(!wasAlreadyReady)) {
+    log('');
+    log('  Note: playwright-cli not available (browser automation will be limited)');
+    log('  Install manually: npm install -g @playwright/cli');
+    log('');
+  }
+
   // Step 3: Config file
   const configCreated = ensureEnvFile();