fix #974

Summary

In browser mode, test failure annotations in the github-actions reporter pointed to the HTTP-served bundle URL (e.g. http://localhost:PORT/@fs/...) instead of the original source file path. This prevented GitHub from correctly mapping errors back to source files.

Root Causes

• BrowserTestRunResult had no getSourcemap implementation — the host controller always returned null, so reporters could never resolve browser stack frames to source files.
• The sourcemap sources entries contained URL-relative paths or webpack:/// prefixes, which the Node.js reporter couldn't resolve to absolute filesystem paths.
• After sourcemap resolution, HTTP frames that failed to map to user source still leaked through the stack filter.

Changes

• Add packages/browser/src/sourceMap/sourceMapLoader.ts — shared source map fetching utility (inline + external .map) with caching, used by both the browser client and the host controller.
• hostController.ts — implement getBrowserSourcemap: loads source maps for browser JS bundles and resolves sources entries (relative paths, webpack:/// prefixes) to absolute filesystem paths. Pass getSourcemap through BrowserTestRunResult so reporters receive real source locations. Fix browser runtime close lifecycle so cleanup runs correctly in all exit paths.
• core/runTests.ts — build a unified getSourcemap that checks browser source maps first, then falls back to node bundler source maps.
• core/utils/error.ts — add defaultResolveSourcePath to handle HTTP-origin frames correctly, add resolveSourcePath option on parseErrorStacktrace, and add a post-resolution filter to drop frames that remain as HTTP URLs (unresolved browser runtime internals).
• Add E2E test e2e/browser-mode/githubActions.test.ts to assert that github-actions reporter annotations point to the correct source file and line.

Related Links

• Closes [Bug]: GitHub Action reporter not working #974

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).