docs(rfc): add qualitative change plan for m6

[huangruiteng]

Summary

Add a qualitative change plan to M6 and stop claiming milestone completion.

• M6 is back to In progress; quality gate pending.
• Add measurable quality gates: quota.py and status.py below 2000 lines,
  heartbeat_prompt.py below 1200 lines, runtime consumption of
  EffectTurn / EffectProgram, no test-only abstraction, ratchets green,
  and Doubao shadow for changed agent-facing packets.
• Add Q1-Q8 phases from parity capture through hot-module extraction and
  runtime consumption.
• Update non-goals so M6 cannot be marked mostly complete before the gates
  pass.

No runtime behavior changes.

Validation

• docs-governance-smoke: passed.
• loopx canary premerge --from-git-diff: passed, self_merge_allowed=true,
  0 manual holds.
• Public boundary scan: passed.

Routing

• continuation-policy: independent_handoff
• excluded-agent: codex-quality-qualification
• claimed-by: codex-side-bypass

[huangruiteng]

Approval conclusion (author-owned PR; GitHub blocks formal self-approval)

Reviewed exact head a2afee7. No blocking findings.

The RFC now requires measurable quality gates before M6 can be called mostly
complete, and provides Q1-Q8 phases for real hot-module extraction and runtime
consumption. Docs only, no runtime behavior changes.

Validation

• docs-governance-smoke: passed.
• loopx canary premerge --from-git-diff: passed, self_merge_allowed=true,
  0 manual holds.
• GitHub dependency-review on this head: pass. Python/build workflows are not
  triggered for a docs-only path change.
• Public boundary scan: passed.

Merge decision: approved after reviewer.