fix(humanize1): bound gen-plan convergence

[DongyunZou]

Summary

• bound every gen-plan planning turn with a backend-neutral wall-clock deadline and finite retries
• preserve the original Convergence(converged, review) contract while validating the five review headings in code
• accept early list-shaped convergence answers during migration without trusting an empty/malformed review
• pass the candidate plan directly to later reviews and stop after two revisions with no material change
• write planner revisions to staging files and atomically promote only validated plans, so late timed-out writes cannot corrupt the durable output
• return a partial plan with the original draft when relevance, analysis, review, candidate generation, or finalization cannot finish
• use Planner/Reviewer terminology and avoid backend-specific tool or identity assumptions

Root Cause

The old flow retried empty/schema-invalid turns forever, had no planning deadline, omitted the original no-material-change stop rule, and sent new reviewers only a file path. A large plan could therefore trigger an unbounded repository re-audit and never produce a durable plan.

Compatibility

• Planning remains the backend-neutral (planner, analyst) shape.
• Existing Convergence(converged, review) answers remain accepted.
• Early list-shaped convergence answers are accepted during migration.
• The flow imports Unrecoverable only through the flow-facing API supplied by humanize2 PR #22.

Verification

• tests/test_gen_plan.py: 10 passed
• flowverse Ruff check and format: passed
• humanize2 main full suite: 1570 passed, 70 skipped
• humanize2 visual worktree full suite: 1606 passed, 70 skipped
• humanize2 all-files pre-commit: passed

Depends on: humanfia/humanize2#22