feat: add Copilot + Edge support, update README

Added copilot.microsoft.com to host_permissions, content_scripts
matches, and BUILTIN_URL_PATTERNS in both Chrome and Firefox manifests
plus the service worker.

Updated README:
- Added Copilot to supported services table
- Added Edge and Brave to browser list
- Added note about desktop apps (can't intercept, use web version)
- Removed old duplicate browser note

https://claude.ai/code/session_01SWSwDfMVij53bCTNSCLMwn

manifest.firefox.json

@@ -20,6 +20,7 @@
     "https://claude.ai/*",
     "https://chatgpt.com/*",
     "https://chat.openai.com/*",
+    "https://copilot.microsoft.com/*",
     "https://grok.x.ai/*",
     "https://x.com/i/grok*",
     "https://gemini.google.com/*",
@@ -36,6 +37,7 @@
         "https://claude.ai/*",
         "https://chatgpt.com/*",
         "https://chat.openai.com/*",
+        "https://copilot.microsoft.com/*",
         "https://grok.x.ai/*",
         "https://x.com/i/grok*",
         "https://gemini.google.com/*",