Add street-cred job unlock gating to job board.

Pushed d1eb8de to main.

What changed

• Added job unlock gating by street cred on play.php.
• Contract cards now display required street cred and visually mark locked jobs.
• Locked jobs cannot be selected in the browser.
• Direct URL run attempts against locked jobs now fail with a clear error instead of silently running something else.

Engine support

• Rules now exposes:
• isJobUnlocked(jobId, streetCred)
• jobsForStreetCred(streetCred)

These helpers make unlock logic reusable beyond the page layer.

Verification

• php tests/run-tests.php -> 53 passed, 0 failed
• Added tests for unlock thresholds (0/3/6/9 path to endgame).
• Smoke checks:
• locked-run guard message appears
• non-run navigation auto-falls back to an unlocked contract