docs(corpflow): Sync CORPFLOW.md to the 4.1.1 contract

[ikorich]

Motivation

CORPFLOW.md targeted the corpflow 4.0.27 stage contract. Since then the contract has changed in several ways: per-row DV ownership with stream artifacts, a required blocks_next_stage, per-task screenshot manifests, consultant-return.v1, the install-root dispatch line, a reserved ## Models heading, and section-length caps. A seam that describes the old contract makes DR/QA fail stages the plugin thinks it passed.

Changes

• Rewritten against the current corpflow plugin-root template. Plugin-specific agents, evidence declaration and build-test command are kept.
• Targets corpflow is now 4.1.1, plus a Consultant return | consultant-return.v1 row, a single ≤300 lines budget, and the Template row dropped.
• The header reserves ## Routing and ## Models for the project-root or user-scope CORPFLOW.md.
• New ### Consultant return — consultant-return.v1 section, plus the template's H3/H4 split so every section stays at or under 1000 characters.
• DR Focus now goes into your row's metadata.artifact.
• The architect consult threshold follows corpflow: High+ (complexity_score ≥31) or an explicit trigger.

Test plan

• corpflow section-lint.sh on CORPFLOW.md: all sections at or under the cap. Line count is within 300.
• No ## Routing/## Models heading, no bare development-N.md, no leftover template placeholders.
• corpflow cross-plugin-refs.bats with this repo as a sibling: 8/8 ok.

Notes

Pairs with IGRSoft/corpflow#466 (corpflow 4.1.1).