fix: Handle non-JSON API responses gracefully

[sentry]

This PR addresses an issue where the browser extension would crash with a SyntaxError: Unexpected token 'u', "upstream c"... is not valid JSON.

The root cause was identified as response.json() being called unconditionally on API responses, even when the response was not ok (e.g., a 502/503 gateway error) and contained a plain-text error message instead of valid JSON.

To fix this, a new private helper method safeResponseJson has been introduced in src/service.ts. This helper:

• Checks response.ok and returns null immediately if the response is not successful.
• Wraps the response.json() call in a try-catch block to gracefully handle parsing errors, returning null if parsing fails.

All four call sites for response.json() in fetchCommitReport, fetchPRComparison, listFlags, and listComponents have been updated to use this.safeResponseJson(response). Additionally, the return objects for these functions now correctly reflect ok: response.ok && data !== null to ensure that callers are aware of failed data retrieval, and setCached calls are guarded to prevent caching null data.

Fixes BROWSER-EXTENSION-Q5

[codecov]

Bundle Report

Changes will increase total bundle size by 216 bytes (0.03%) ⬆️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
codecov-browser-extension-array-push	649.3kB	216 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	216 bytes	198.6kB	0.11%