docs(policy): correct ephapax Admitted count (3 → 1) + link adoption PR (#221)

## Summary

The trusted-base reduction policy's P0 migration table cited **3
Admitteds** in `ephapax/formal/Semantics.v`. The actual count on `main`
is **1** — the other two (`step_preserves_type` and
`step_output_context_eq`) were discharged via
[ephapax#146](hyperpolymath/ephapax#146) (Path 3
at-pre helper landing) before this policy doc was filed.

Also adds:
- Link to `formal/PRESERVATION-DESIGN.md` (four-layer redesign on branch
`proof/l1-region-threading-design`) as the principled closure plan.
- Forward link to
[ephapax#164](hyperpolymath/ephapax#164) — the
P0 migration PR adopting this policy in `ephapax/docs/proof-debt.adoc`.

No semantic change to the policy itself — just keeping the migration
table accurate as repos adopt the schema.

## Test plan

- [x] One-line `.adoc` table cell edit; no build target affected
- [x] GPG-signed commit (key `4A03639C…2867091E`, noreply email)
- [x] Auto-merge SQUASH enabled

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Author: hyperpolymath

docs/TRUSTED-BASE-REDUCTION-POLICY.adoc

@@ -191,7 +191,7 @@ first (rough P0/P1/P2 ordering):
 |===
 | Priority | Repo | Why this one first
 
-| P0 | `ephapax`             | 3 `Admitted`s in `formal/Semantics.v` already have a discharge plan (memory: `project_ephapax_preservation_closure_plan`); annotate while closing.
+| P0 | `ephapax`             | 1 `Admitted` in `formal/Semantics.v` (`preservation`); was 3 at audit time, 2 discharged via https://github.com/hyperpolymath/ephapax/pull/146[ephapax#146]. Discharge plan in `ROADMAP.adoc` § "Preservation closure plan" + `formal/PRESERVATION-DESIGN.md` (four-layer redesign on branch `proof/l1-region-threading-design`). Migration filed: https://github.com/hyperpolymath/ephapax/pull/164[ephapax#164].
 | P0 | `boj-server`          | Reference implementation — formalise the existing harness as the canonical example.
 | P1 | `absolute-zero`       | 72 Coq + 315 Lean markers across 6638 proof files; needs the schema before any single-repo close-out is tractable.
 | P1 | `maa-framework`       | 134 markers in 25 files (high density); investigate whether vendored or original.