Switch to HTTP Basic Auth and improve PDF detection

- Replace token-based auth with HTTP Basic Authentication per Binect API v1 spec
- Improve PDF detection: check current tab first, then background service, fallback to recent downloads
- Add password visibility toggle in login form
- Add extensive debug logging throughout for troubleshooting
- Update manifest with alarms, activeTab permissions and <all_urls> host permission
- Add documentation files and development helper scripts
- Add Binect API specs for reference

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

public/manifest.json

@@ -6,14 +6,16 @@
   "default_locale": "en",
   "permissions": [
     "downloads",
-    "storage"
+    "storage",
+    "alarms",
+    "activeTab"
   ],
   "host_permissions": [
-    "https://api.binect.de/*"
+    "https://api.binect.de/*",
+    "<all_urls>"
   ],
   "background": {
-    "service_worker": "background.js",
-    "type": "module"
+    "service_worker": "background.js"
   },
   "action": {
     "default_popup": "popup.html",