feat: add stale-safe LangGraph resume

[aantenore]

Outcome

Adds an optional LangGraph integration that resumes paused effects through authoritative revalidation, one idempotent lease, one durable target attempt, and an explicit same-attempt recovery gate.

Also adds SQLite schema v3 lease-request bindings, minimized checkpoint state, stage-specific redacted outcomes, migration coverage, architecture documentation, and a current competitive boundary.

Verification

• 170 tests pass
• 90.21% branch coverage
• Ruff format and lint pass
• mypy strict passes
• wheel and sdist checks pass
• core-only, LangGraph-extra, Python 3.11, and Python 3.13 install smoke tests pass
• deterministic artifacts reproduce byte-for-byte
• dependency audit reports no known vulnerabilities
• commit metadata uses the canonical personal identity