Allow bounded lifecycle overrides for exact TV episodes

[cbusillo]

Summary

• allow an explicitly selected TV episode to borrow its parent-season lifecycle hold override
• keep candidate selection and the generated manifest bounded to that exact file
• preserve hold reasons and manual-override provenance in the manifest
• document the exact-episode override contract

Why

The controlled #256 seed sequence is exact-item scoped. A prior verified promotion refreshed Bluey Season 2's acquisition hold through September 18, 2026. The existing API could override only a whole season, which would violate the fixed pilot ordering. This change provides the missing bounded path without altering saved lifecycle policy or queueing siblings.

Validation

• uv run --with pytest pytest -q tests/test_encode_queue_recovery.py -k lifecycle_override — 2 passed
• uv run --with pytest pytest -q tests/test_library_lifecycle.py tests/test_web_route_security.py — 30 passed
• uv run --with pytest pytest -q tests/test_encode_queue_recovery.py — 582 passed, 8 subtests passed
• bash scripts/pre-commit-check.sh — passed; 1,655 backend tests passed, 2 skipped, frontend/package/CLI/browser gates green
• commit hook reran the full acceptance gate successfully
• PyCharm changed-file inspection — UNKNOWN because project analysis never became ready after the helper's maintained retries; zero problems were captured, but the result is not treated as GREEN

Refs #256