fix(gbrain): parse refresh detection without Python path dependency

[maxpetrusenkoagent]

Summary

• fixes gstack-config gbrain-refresh so the detection summary no longer depends on Python opening the detection file path
• parses the flat gbrain-detection.json status/version fields with shell grep/sed first, then keeps Python only as a fallback
• adds a regression test with a fake PATH python3 that fails like native Windows Python does on MSYS-style paths

Closes #1967

Verification

• bun test test/gstack-config-gbrain-refresh.test.ts (failed before the fix, passes after)
• bash -n bin/gstack-config
• bun test test/gstack-config-gbrain-refresh.test.ts test/gstack-config-redact-keys.test.ts
• Windows CI subset equivalent plus new regression:
  bun test test/gstack-paths.test.ts browse/test/claude-bin.test.ts test/test-free-shards.test.ts browse/test/file-permissions.test.ts browse/test/security.test.ts browse/test/server-sanitize-surrogates.test.ts test/setup-windows-fallback.test.ts test/build-script-shell-compat.test.ts test/docs-config-keys.test.ts test/brain-sync-windows-paths.test.ts make-pdf/test/browseClient.test.ts make-pdf/test/pdftotext.test.ts test/gstack-config-gbrain-refresh.test.ts
• Local autoreview subagent: clean, no blocking findings

Notes

• I also tried bun run test:windows; it failed in existing browse/test/terminal-agent.test.ts on a source-level guard unrelated to this diff. The actual Windows workflow's curated file list plus the new regression passes locally.

[maxpetrusenkoagent]

Hermes verification note

Autoreview against the exact PR diff is clean.

Verification run locally:

• bun test test/gstack-config-gbrain-refresh.test.ts failed before the fix and passes after
• bash -n bin/gstack-config
• bun test test/gstack-config-gbrain-refresh.test.ts test/gstack-config-redact-keys.test.ts
• Windows workflow subset equivalent plus this regression:
  bun test test/gstack-paths.test.ts browse/test/claude-bin.test.ts test/test-free-shards.test.ts browse/test/file-permissions.test.ts browse/test/security.test.ts browse/test/server-sanitize-surrogates.test.ts test/setup-windows-fallback.test.ts test/build-script-shell-compat.test.ts test/docs-config-keys.test.ts test/brain-sync-windows-paths.test.ts make-pdf/test/browseClient.test.ts make-pdf/test/pdftotext.test.ts test/gstack-config-gbrain-refresh.test.ts

Reviewer state:

• GitHub reports no checks on this fork branch, so I ran explicit Codex autoreview against gh pr diff #1981.
• Codex verdict: clean, no blocking findings.

Known unrelated local gate note:

• bun run test:windows currently fails in existing browse/test/terminal-agent.test.ts source-level guard. This PR does not touch browse/src/terminal-agent.ts or that test, and the actual Windows workflow's curated file list plus the new regression passes locally.

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