Track filled applications and show existing application records

[kensac]

Changes

• Save a populated application fill to the personal board through the shared import service, without setting application status or date.
• Canonicalize supported posting URLs, reuse existing jobs, preserve notes and hidden state, and share extraction task admission.
• Link the fill and board save atomically; publish board state after commit.
• Show the current user’s saved status, application date and confirmed fill submission before autofill.
• Leave the employer form intact and offer retry when board saving fails.
• Package extension 0.3.6 and regenerate the API contract.

Verification

Both backend regressions failed against the old code in CI. All three new browser regressions failed against extension 0.3.5. Typecheck, build, unit tests and all 31 browser tests pass locally. Backend tests run in CI, including ownership and private-upload isolation. No production data was modified and no employer application was submitted.