test(miner-foundation): engine-parity fixture corpus for predicted-gate

[JSONbored]

Build the shared FIXTURE corpus the parity suite (a separate follow-up issue) will run against: a set of representative PredictedGateInput + FocusManifest + RepositoryRecord/IssueRecord/PullRequestRecord combinations covering the gate's major branches (clean pass, duplicate-PR block, missing-linked-issue block, manifest-blocked-path, low-readiness warn, oss-anti-slop pack vs gittensor pack, with-changed-paths vs without). This issue is fixtures-only — no assertion harness yet — so it can land independently and the parity-runner issue can consume it without also having to invent representative scenarios under time pressure.

Deliverables

• test/fixtures/engine-parity/predicted-gate/ directory with one JSON (or .ts object-literal) fixture file per scenario (aim for 8-10 scenarios covering the branch list above).
• Each fixture is a complete, self-contained input to buildPredictedGateVerdict (no external state needed) plus a comment noting which gate branch it exercises.
• A short test/fixtures/engine-parity/predicted-gate/README.md (or a top-of-file comment in an index fixture) listing every scenario and the specific finding code(s) it is expected to produce, so a reviewer can sanity-check coverage without running the suite.
• A smoke test (test/unit/engine-parity-fixtures.test.ts) that merely loads every fixture file and asserts it parses/type-checks — catching a malformed fixture before the parity-runner issue depends on it.

References

• src/rules/predicted-gate.ts (263 lines) — the function under test; its branch structure (lines 149-247) enumerates the scenarios to fixture.
• test/fixtures/local-scorer/ — existing fixture-directory convention in this repo to mirror (naming, one file per scenario).
• src/types.ts — RepositoryRecord/IssueRecord/PullRequestRecord/BountyRecord shapes the fixtures must conform to.

[linear-code]

JSO-2382