docs: update phase4-plan.md to reflect Phase 3 closure + discoveries

[rafael5]

Summary

Phase 3 closed 2026-05-11 (PRs #19 / #20 / #22 / #23 / #24 — see docs/phase3-evidence.md). The Phase 4 plan was written before Phase 3 shipped and assumed Track B would block on it. This PR folds Phase 3's actual landings back into docs/phase4-plan.md.

What changed

• §0 dependency table — Phase 3 row flipped 🟡 In flight → ✅ CLOSED. Captures the importable helper list (match_intent, parse_typed_id, resolve_module_manifest_url, find_module_entry, entry_has_signature_and_example, fetch). Verification snippet rewritten to invoke make handshake / make recipes-check (now real Make targets).
• §0 narrative — drop "Phase 4 may start at Phase 3 C2"; all three upstream phases are closed and Track B is fully unblocked.
• §1 Track Index — Track B's Blocked by simplifies to A7 (was A7 ∧ Phase 3 C2).
• §1 new subsection "What Phase 3 already shipped that Phase 4 consumes" — a 5-row table of the concrete artifacts Track B / Track E pull from .github/main (helpers, offline fixtures, recipe schema + 4 recipes, the two Make targets, recipe runner pattern), plus the two known out-of-scope follow-ups (YAML parser limitations, orphan fixtures) noted as non-blocking.
• §3 B1 — fixtures point at Phase 3's bundled set under profile/build/fixtures/ instead of "a frozen snapshot".
• §3 B2 — route_intent reshapes to vendor-and-fallback (Phase 3's match_intent handles exact matches; only the fuzzy-rank fallback is genuinely new code).
• §3 B3 — describe("recipe:new-app-tdd-ci") is no longer hypothetical; cites the real recipe + the task_index.json recipes category.
• §3 B4 — spell out which helpers describe reuses vs which path is new (the recipe: ID lookup).
• §6 Track E — collapses to one evidence doc following Phase 1 + Phase 3 convention. Drop phase4-status.md; fold the stage roll-up into phase4-evidence.md. Rename .txt → .md for parity.
• §7 Stage Matrix — B1 simplified; E2 (status doc) removed; E1 verification rewritten; E3 → E2.
• §9 Risk Notes — replace "Phase 3 dependency timing" (historical) with "Vendored Phase 3 helper drift" — the new ongoing risk + TDD-based mitigation.
• §10 Gantt — phase 3 lane shows ✅ CLOSED 2026-05-11.
• §11 Done definition — 10 → 9 criteria (status doc removed); evidence file renamed; "every §11 done-criterion cited green" added.

What did NOT change

Scope, exit criterion (canonical-query round-trip from a fresh uvx --from git+...@v0.1.0 install), GitHub-Release-over-PyPI distribution decision, and the 5-track layout (A / B / C / D / E) all stand.

Test plan

• Markdown-only change; no CI surface touched
• Internal cross-refs (phase3-evidence.md, profile/build/fixtures/, recipe.schema.json, the 4 shipped recipes) verified to exist on main
• CI green