refactor: strip WP-/RB- ticket refs from backend (RD-19)

The backend half of the sweep RD-18 did for the front end. git blame
holds the provenance and stays correct when the code moves; the
comment names a closed ticket and tells the reader nothing the
sentence around it does not.

public/letter.css and LetterHtml.golden.html change together, because
the renderer inlines the CSS and the golden file snapshots the
result.

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

backend/tests/BigRegister.Tests/RouteInventoryTests.cs

@@ -4,11 +4,11 @@ using Microsoft.Extensions.DependencyInjection;
 
 namespace BigRegister.Tests;
 
-/// RB-12/BIO-016 (BL-006 — "the backend has zero automated architecture enforcement"): the
+/// BIO-016 (BL-006 — "the backend has zero automated architecture enforcement"): the
 /// only thing that used to keep an admin-shaped endpoint behind `Authz` was a human noticing
 /// in review. BIO-003 (`X-Admin`, a second gate outside `Authz`) and BIO-004 (two endpoints
 /// with no gate at all) are exactly the failure mode this test is a safety net for — and it is
-/// the safety net RB-19 (a 900-line `Program.cs` reorder) leans on, so its value is entirely in
+/// the safety net a 900-line `Program.cs` reorder leans on, so its value is entirely in
 /// being hard to fool.
 ///
 /// Every mapped route must be accounted for exactly one of two ways:
@@ -48,14 +48,14 @@ public class RouteInventoryTests(TestWebApplicationFactory factory) : IClassFixt
     new("GET", "/api/v1/duo/diplomas", "Static DUO reference fixture + manual-diploma policy — same for every caller."),
     new("GET", "/api/v1/intake/policy", "Config VALUE shipped for instant FE feedback (ADR-0001); the server re-validates as authority."),
     new("GET", "/api/v1/uploads/categories", "Static per-wizard category config, no PII, no per-caller distinction."),
-    new("GET", "/api/v1/flags", "Feature-flag catalog + state, readable by any principal by design (WP-47) — only the PUT toggle is admin-gated."),
+    new("GET", "/api/v1/flags", "Feature-flag catalog + state, readable by any principal by design — only the PUT toggle is admin-gated."),
     new("GET", "/api/v1/me", "Reflects only the ACTING caller's own role-derived capabilities — no other caller's data to leak."),
 
     // --- Citizen-submitted writes / ownership-scoped inline (ctx.Zorgverlener()/ctx.Caller()),
     // not a role-only admin wrapper because the boundary is resource ownership, not a role. ---
     new("POST", "/api/v1/change-requests", "Citizen submission; Submit() records outcome + idempotency, attributed to the acting caller."),
     new("POST", "/api/v1/uploads", "Upload is attributed to ctx.Zorgverlener() as owner — there is no pre-existing resource to own yet."),
-    new("GET", "/api/v1/uploads/{documentId}/content", "Ownership-scoped inline (RB-01/BIO-004): owning citizen, or a behandelaar via Authz.CanBeoordelen."),
+    new("GET", "/api/v1/uploads/{documentId}/content", "Ownership-scoped inline (BIO-004): owning citizen, or a behandelaar via Authz.CanBeoordelen."),
     new("GET", "/api/v1/uploads/status", "Ownership-scoped inline: DocumentStore.ByLocalIds filtered to ctx.Zorgverlener().Bsn."),
     new("DELETE", "/api/v1/uploads/{documentId}", "Ownership-scoped inline: DocumentStore.DeleteOwned keyed by ctx.Zorgverlener().Bsn."),
     new("GET", "/api/v1/aanvragen", "Ownership-scoped inline: IZaakSource.ListMyCases(ctx.Zorgverlener(), ...)."),
@@ -72,14 +72,14 @@ public class RouteInventoryTests(TestWebApplicationFactory factory) : IClassFixt
     // enforce/emit twin for this whole surface (Authz.CanActOn via BriefStore, ToView's
     // Decisions dto) — a different single-source-of-truth than the five Program.cs wrappers,
     // not a missing one. ---
-    new("GET", "/api/v1/brief", "Ownership-scoped inline: BriefStore.Get(ctx.Zorgverlener().Bsn), 404 when absent (RB-23)."),
+    new("GET", "/api/v1/brief", "Ownership-scoped inline: BriefStore.Get(ctx.Zorgverlener().Bsn), 404 when absent."),
     new("PUT", "/api/v1/brief", "Brief status-machine enforcement: BriefStore.Save + Authz.CanActOn (drafter-only)."),
     new("POST", "/api/v1/brief/submit", "Brief status-machine enforcement: BriefStore.Submit + Authz.CanActOn."),
     new("POST", "/api/v1/brief/approve", "Brief status-machine enforcement: BriefStore.Approve + Authz.CanActOn (approver != drafter)."),
     new("POST", "/api/v1/brief/reject", "Brief status-machine enforcement: BriefStore.Reject + Authz.CanActOn."),
     new("POST", "/api/v1/brief/send", "Brief status-machine enforcement: BriefStore.Send; not role-gated today, per the endpoint's own comment."),
     new("POST", "/api/v1/brief/reveal-bignummer", "Own inline capability + step-up check (Authz.CanRevealBigNummer + X-Step-Up), audited directly."),
-    new("GET", "/api/v1/brief/preview", "Ownership-scoped inline: BriefStore.Get(ctx.Zorgverlener().Bsn), 404 when absent (RB-23); hand-written FE fetch."),
+    new("GET", "/api/v1/brief/preview", "Ownership-scoped inline: BriefStore.Get(ctx.Zorgverlener().Bsn), 404 when absent; hand-written FE fetch."),
     new("POST", "/api/v1/brief/reset", "Deliberately unguarded demo affordance — the endpoint's own comment says so: 'showcase affordance only'."),
   ];