fix: Prevent TypeError from orphaned content script

[sentry]

This PR addresses a TypeError: Cannot read properties of undefined (reading 'local') that occurs in the GitHub file content script (src/content/github/file/main.tsx).

Root Cause:
In Chrome Manifest V3, when the browser extension is reloaded or updated while a content script is already running on a tab, the extension context for that content script becomes invalidated. This causes browser.storage (which is a polyfill for chrome.storage) to become undefined. Subsequent attempts to access browser.storage.local then throw a TypeError.

Solution:
To prevent this, a new helper function isExtensionContextValid() has been introduced. This function checks browser.runtime?.id, which will be undefined if the extension context has been invalidated. The main() function in src/content/github/file/main.tsx now calls this validity check at its entry point. If the context is invalid, main() will return early, preventing any access to browser.storage.local and gracefully handling the orphaned content script scenario. This protects both initial page loads and subsequent soft-nav:end events from triggering the error.

Fixes BROWSER-EXTENSION-SH

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[codecov]

Bundle Report

Changes will increase total bundle size by 176 bytes (0.03%) ⬆️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
codecov-browser-extension-array-push	660.64kB	176 bytes (0.03%) ⬆️

Affected Assets, Files, and Routes:

view changes for bundle: codecov-browser-extension-array-push

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
background.js	89 bytes	207.75kB	0.04%
githubFile.js	87 bytes	11.55kB	0.76%

Files in githubFile.js:

• ./src/content/github/file/main.tsx → Total Size: 11.97kB