Support external application answer context and keep the panel open

[kensac]

Changes

• Fetch missing posting context for an owned application fill from supported hosted Ashby, Greenhouse and Lever public APIs.
• Keep jobs outside the catalog outside the catalog; no board membership is required or created.
• Restrict fetching to known ATS hosts and canonical token paths. Unsupported or unavailable posting context stays explicit instead of inventing company details.
• Keep the extension panel open when navigating to an unanswered field. Manual minimize remains available.
• Package extension version 0.3.5.

Verification

The external-context regression failed against the old backend in CI. The no-collapse browser regression failed against the old extension locally. Typecheck, build, unit tests and all 28 browser tests pass locally after the change. The public Ivo endpoint returned the relevant 3,895-character posting description. Fixed backend tests run in CI. No live model call or employer form submission was made.