Expand public job APIs and harden scoped reads and execution services

[featherenvy]

Producers and workers can now share job specifications and typed payload contracts, while operational callers can select explicit global, tenant, or administrative read scopes. Handlers gain deadline budgets and fenced progress/checkpoint services; compact summary pagination, enqueue outcomes, migration identity, and fluent DAG helpers round out the public API additions.

The branch also preserves index access for scoped reads, validates durable progress atomically, reduces redundant progress locking and workflow persistence statements, and bounds test database startup. The README and changelog document compatibility changes and the required pagination migration, including its queue-write blocking deployment window.

Validation on PostgreSQL 18.6:

• Workspace tests: 915 passed, zero failed, five explicitly ignored; the progress cost diagnostic also passed when run explicitly.
• Full lint script and four packaged consumer smoke tests passed.
• SQLx metadata refreshed and synchronized across all three cache directories.
• Focused query-plan, deadline, cancellation, lease-expiry, and migration regressions passed.
• Independent Claude, Codex, and Cursor branch reviews completed; Cursor covered 67 of 68 scope pages. The final actionable changelog omission is fixed.

Detailed research, measurements, and validation limitations are recorded in docs/review-hot-path-fixes-2026-09-05.md. Downstream application suites were not rerun. Broader run-ID indexing and consumer-adoption investigations remain tracked separately in Beads.

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