feat(v3): exemptions + CI awareness + round tracking + audit-paths prompt

[ashbrener]

Summary

Four upgrades to the codex-review pre-push hook (hook version stamp 2 -> 3):

• Exemption file (.wingman-exemptions.yaml) — codex sees ratified out-of-scope decisions and stops re-flagging them. Sample shipped at assets/.wingman-exemptions.yaml.sample; installer copies it to the user's repo as .wingman-exemptions.yaml.sample (NEVER auto-creates the active file).
• CI status awareness — after the review, hook calls gh pr checks and prepends a synthetic [P1] finding if a required check is RED, so the next remediation round addresses CI-red instead of bandaging code that's locally green.
• Round tracking + convergence detection — .reviews/_convergence.json ledger; emits [CONVERGENCE NOTICE] when the stop-rule fires (0 P1 + <=2 P2 for 2 consecutive rounds) or [STAGNATION ALERT] when the same finding flags twice in a row.
• Audit-related-paths prompt — codex now audits code paths importing from / imported by the changed modules in the same review, surfacing same-class defects together.

Rationale

Direct lessons from project-arc spec 004's 12-round wingman convergence. Each gap was felt for 3+ rounds before being addressed by hand:

Round	Pain
1-3	Codex re-flagged "preserve old import paths via shims" 3 times despite constitution v0.1.3 rejecting it -> Feature 1
All 12	quality-gate required check was red the entire time, wingman never noticed -> Feature 2
1-12	No "are we done yet?" signal -> Feature 3
4-8	Each fix introduced 1-2 same-class bugs in neighbouring files codex saw next round -> Feature 4

Full feature write-up: docs/wingman-v3-features.md. Schema bump documented in README.

Test plan

• CI green: lint (shellcheck), syntax (bash -n + py_compile of both embedded heredocs), install-smoke (6 scenarios — fresh / v1->v3 upgrade / v2->v3 upgrade / --force / exemption parsing / convergence ledger schema)
• Local: bash -n scripts/install.sh && bash -n assets/pre-push.sample -> clean
• Local: shellcheck --severity=error on both -> clean
• Local: v2 -> v3 upgrade in tmp repo via install.sh -> v3 marker present, exactly 1 wingman block, exemption sample copied
• Local: exemption file parsed without PyYAML; rendered prompt includes id + rationale + banner
• Local: _convergence.json schema matches spec — branch, rounds[], convergence{stop_rule, trend, stagnation}; stop-rule fires correctly at round 3 of 0,0,0 P1
• Manual: install on a real consumer (project-arc) post-merge and run a real codex review with a populated .wingman-exemptions.yaml

Stays DRAFT

This PR stays DRAFT per workflow policy — only the human un-drafts after review.