Fix badge and popup count synchronization

[alex-w-developer]

Summary

• replace Chrome's unreadable automatic DNR badge with a production-safe extension-owned badge
• mirror the popup's active metric: estimated blocks in normal mode and decoyed requests in Decoy Mode
• synchronize badge state on navigation, report updates, and mode changes
• document the counter behavior and add real-browser regression coverage

Root cause

Chrome displays the automatic declarativeNetRequest action count, but chrome.action.getBadgeText() returns only a placeholder unless the extension requests declarativeNetRequestFeedback. GetBlocked! intentionally forbids that debug-sensitive permission, so the popup could not recover the number shown on the badge.

Validation

• npm run check
• npm run test:browser — 17 passed
• git diff --check

Closes #10