feat: add Chrome DevTools Protocol browser tools

Add BrowserManager (puppeteer-core) with page pool and auto-detection of
Chrome/Chromium. Six tools: browser.navigate, browser.screenshot,
browser.click, browser.type, browser.content, browser.eval. Feature is
opt-in (browser.enabled defaults to false). Add to coding tool profile.
Includes 22 unit tests for manager and all tools.

src/tools/policy.ts

@@ -35,6 +35,12 @@ const PROFILE_TOOLS: Record<ToolProfile, Set<string>> = {
     'process.output',
     'process.kill',
     'process.list',
+    'browser.navigate',
+    'browser.screenshot',
+    'browser.click',
+    'browser.type',
+    'browser.content',
+    'browser.eval',
   ]),
   full: new Set(), // Special: matches everything
 };