Fix: Keep service worker alive using content script port connection

[adervark]

Problem

Fixes #30 - The Manifest V3 service worker becomes inactive after idle time, causing submissions to fail unless DevTools is open.

Solution

• Added a content script that runs on all Codeforces pages and maintains a chrome.runtime.connect() keep-alive port connection
• Added port connection handling in the background script to track connected ports
• Added tab load waiting before sending submit messages to prevent race conditions

Changes

File	Change
src/contentScript.ts	NEW - Keep-alive port on CF pages
src/backgroundScript.ts	Added port connection handling
src/handleSubmit.ts	Wait for tab load before sending message
webpack.config.js	Added contentScript entry point
manifest-chrome.partial.json	Added content_scripts section
manifest-firefox.partial.json	Added content_scripts section

How it works

1. Content script runs on Codeforces pages at document_start
2. Establishes keep-alive port with chrome.runtime.connect()
3. Port connection keeps service worker active in MV3
4. Message sending now waits for tab to fully load

Testing

• ✅ Service worker stays active while Codeforces tabs are open
• ✅ Submissions work without DevTools open

[adervark]

@agrawal-d could you please take a look at this