feat: settle generations after service readiness

[cristianoliveira]

Problem

A healthy long-running service keeps its generation running forever, so a completed pipeline never reports success.

Changes

• add explicit bounded jobs[].readiness commands
• settle a generation after finite work and service readiness pass
• keep the ready service alive in a worker-owned pool
• preserve immutable generation results when service state later changes
• expose minimal secondary services: [{ name, state }] status
• safely hand off, replace, cancel, restart, and reap managed service processes
• print the normal terminal summary exactly once
• update lifecycle documentation and Pi watcher decoding

Expected output

Success; Completed: 1; Failed: 0; Duration: N.NNNNs

Generation result remains primary; service status is secondary.

Verification

Passed:

• Rust formatting and 863 library tests
• full cargo test --features test-integration
• all 20 control_await integration tests
• readiness pass/timeout, post-settlement failure, unrelated continuity, cancellation, SIGTERM, and no-overlap service replacement
• Pi watcher format, lint, typecheck, and 527 tests

The no-overlap replacement regression found while opening this draft was fixed in 5840ab0 on this rebased branch.

Remaining before ready/merge

• readiness-aware valid/invalid reload proof
• supersession breadth
• hook/output agreement
• fresh watcher target evidence
• independent QA

Stack and companion PR

• Base PR: feat: correlate settled failure hooks #290
• Pi watcher companion: feat: show readiness service status carbon-ni/pi-watcher#1

Tracking

TASK-0161 is complete. TASK-0162 remains in progress for the remaining proof and final gates.