docs: close WP-72..75, regenerate behaviour spec

Four close-outs and their README rows. The behaviour spec is regenerated
once here rather than per-track — it derives from every test name in the
repo, so any track running it would have conflicted with the other three.

Records two findings the arc surfaced but did not cause: the /brief/preview
staleness for non-DemoOwner identities (blocking per-spec identity isolation
in brief-v2.spec.ts), and that WP-72/73 had to share a commit because both
edit Program.cs — separate execution waves prevented build collisions but
did not produce separable diffs.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/project/backlog/WP-75-fe-be-seam-closure.md

@@ -0,0 +1,65 @@
+# WP-75 — Close the remaining FE/BE seams
+
+Status: done (6fa27d1)
+Phase: 12 — DDD hardening
+
+## Why
+
+WP-71 added `scripts/check-seam.sh` guarding one literal pair (the scholing threshold) and
+documented three further FE/BE duplications that nothing tested across the seam. This closes
+them — two by deletion, one by a guard, one by an actual fix.
+
+## Decisions (pre-made)
+
+1. **Dead reference impls get deleted, and `CLAUDE.md` is amended.** This overturns the
+   documented policy that server-owned rules "stay in `domain/*.policy.ts` as reference impl +
+   unit test". That policy is precisely what kept dead code alive. Blast radius is small:
+   `registration.policy.ts` is the only `*.policy.ts` in the repo.
+2. Guard the `Besluit` tag list by **extending** `check-seam.sh`, not adding a second script.
+3. The phone seam gets a **contract test**, not a grep check — see below.
+
+## Acceptance criteria
+
+- [x] `isHerregistratieEligible` deleted (uncalled; dead by its own doc-comment) along with
+      `isStatusConsistent` (also uncalled — WP-71 had added a spec for it the session before).
+      The three live exports (`statusLabel`, `statusColor`, `herregistratieDeadline`) stay, and
+      `herregistratieDeadline` gained direct coverage it previously only had transitively.
+- [x] `CLAUDE.md` amended: server-owned rules live **only** on the server; the FE may mirror a
+      server-supplied _value_ (a threshold, a bound) for instant feedback, but never
+      reimplements the _algorithm_. ADR-0001's matching claim aligned.
+- [x] `check-seam.sh` guards the `Besluit` tag list, **proven to fail** when a fourth member is
+      added to the C# enum only, naming both files and both lists. Anchored on the full
+      declaration so it avoids the "greps all matches" trap WP-69 documented.
+- [x] Phone contract test added and green; backend stripping fixed.
+
+## The phone divergence was real, not latent
+
+WP-71 recorded this as latent because the Angular app normalises before sending — true of _that_
+path. The contract test proved the two sides genuinely disagreed: the backend returned **422**
+for `+31612345678` and `(06) 12345678`, both of which the FE's own `parseTelefoonnummer`
+accepts. Any non-Angular client, crafted POST, or future FE change would have hit it.
+
+`SubmissionRules.RejectPhoneChange` now strips exactly what the FE strips (`[\s\-()]`, then a
+leading `+31` → `0`) before applying the shared `^0\d{9}$`. The FE value object was not touched —
+it is the more permissive and correct side.
+
+**Why a contract test rather than a grep check:** both sides carry the identical `^0\d{9}$`
+literal, so a drift check would have compared them, found them equal, and reported all clear.
+The divergence was in the _normalisation before_ the regex — invisible to text comparison. Worth
+remembering when choosing between the two guard styles: grep checks catch drifting **constants**,
+contract tests catch drifting **behaviour**.
+
+## Verification
+
+```bash
+npm run check:seam    # both checks OK
+npm run ci
+cd backend && dotnet test BigRegister.slnx --filter "Category!=Integration"
+```
+
+## Follow-ups
+
+- Making `Besluit` flow through the generated client as an enum rather than a `string` would
+  remove that seam entirely rather than guarding it — a wire change, so not done here.
+- The herregistratie-eligibility seam is closed by deletion; if a FE mirror is ever reintroduced,
+  the disjoint-fixture problem returns and would need a contract test, not a grep check.