fix: separate freshness from scoring semantics

[pashawkola33]

What changed

• Exclude vacancy freshness from the persisted semantic fit score while keeping freshness observable for recency/explanation.
• Prevent vacancies with zero confirmed Java/backend evidence from reaching the POSSIBLE_MATCH threshold.
• Introduce semantic ScoreCard equality for preview/rescore planning so freshness-only drift does not create rescore work.
• Keep persisted rescore state checks strict while allowing recomputed freshness metadata to drift safely between preview and write.
• Version the rescore plan fingerprint to v2, using exact stored state and semantic computed state.
• Update affected preview/write fixtures and add scoring/rescore regression contracts.

Why

Formal eligibility and supporting tooling could previously push non-backend roles into POSSIBLE_MATCH even with no Java/backend evidence. Freshness also changed the persisted compatibility score solely as time passed, which made semantic scores and rescore plans time-dependent.

Validation

Focused regression suite passed: 92 tests, 0 failures, 0 errors, 0 skipped.

Also verified:

• git diff --check clean
• one commit on top of 7134d763ab79bdb816bfbe7d03c0a5227904e0e7
• clean worktree before push
• pushed branch SHA: 705a4470245b1242892bd99a51e2381890b224c3

No production rescore/write or deployment action is part of this PR.