Add Chrome DevTools extension for anti-pattern detection

Adds a Manifest V3 Chrome extension that injects the detector when
DevTools opens, with a dedicated panel for browsing findings, a toolbar
popup for quick scan/toggle, and per-rule settings synced via
chrome.storage. Categorizes anti-patterns into AI slop vs quality
issues with visual differentiation (sparkle prefix, panel grouping).
Overlay labels are polished with flush positioning, cycling for
multi-finding elements, and synchronized hover darkening.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

extension/devtools/devtools.js

@@ -0,0 +1,21 @@
+/**
+ * Impeccable DevTools Extension - DevTools Page
+ *
+ * Creates the Impeccable panel and triggers an auto-scan when DevTools opens.
+ * This page lives for the entire DevTools session -- its port disconnect
+ * is the canonical signal that DevTools has closed.
+ */
+
+chrome.devtools.panels.create(
+  'Impeccable',
+  'icons/icon-32.png',
+  'devtools/panel.html'
+);
+
+// Connect a lifecycle port so the service worker knows when DevTools closes
+const port = chrome.runtime.connect({
+  name: `impeccable-devtools-${chrome.devtools.inspectedWindow.tabId}`,
+});
+
+// Auto-scan when DevTools opens (regardless of which panel is active).
+port.postMessage({ action: 'scan' });