fix(brief): keep the dev hatches out of production builds (RB-11)

BIO-012: roleInterceptor/subjectInterceptor are correctly registered
only under isDevMode(), but three hand-written fetch adapters
(reveal-bignummer, letter-preview, org-template's proefbrief) bypass
HttpClient and set X-Role/X-Subject themselves with no guard. The
readers underneath, role.ts and subject.ts, were ungated too: they
read ?role=/?subject= and wrote it into sessionStorage on any
navigation, in any build -- for ?subject= that value is a BSN, which
is exactly what SessionStore's G1 comment promises never happens.

Gate both layers: currentRole()/currentSubject() return their safe
default immediately outside isDevMode() (no query-param read, no
sessionStorage write), and the three adapters additionally wrap their
headers in isDevMode() so a production request carries neither header
at all, matching what an HttpClient request already does once the
interceptors aren't registered.

TE-002: reveal-bignummer's response-shape validation was a "Trust
boundary" a spec could only reach by stubbing globalThis.fetch.
Exported it as parseRevealed(body), matching the other 30 parse*
boundaries in the repo. Same treatment for letter-preview's
errorMessage and org-template's proefbrief error mapping (extracted
from an inline try/catch into a named, exported function first, since
it wasn't already separate).

BIO-006(a): reveal-bignummer sent X-Step-Up: 'true' unconditionally,
so the backend's step-up precondition constrained nothing. reveal()
now takes a stepUp flag; BriefStore.revealBigNummer() -- reachable
only after the UI's confirm() gesture -- is the one that supplies it,
so the literal no longer lives in the transport adapter.

BIO-006(b): documented in roles-and-access.md that drafter is also
the backend's fallback identity (StubIdentityProvider's catch-all
arm), not just the dev switcher's initial choice -- so the
least-privilege consequence of it also being the only role that may
reveal a BSN is visible.

Doc correction, same diff: roles-and-access.md's "wired only under
isDevMode()" claim was false for the three hand-written fetch paths;
it now says where the gate lives (interceptor registration and the
reader functions) so it doesn't go stale the same way again.
CLAUDE.md's dev-only claims needed no correction -- they already
noted these three calls bypass the interceptor.

Every fix has a test confirmed red by temporarily reverting the
source change and rerunning the suite before restoring it.

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

apps/ssp/src/app/brief/application/brief.store.ts

@@ -233,9 +233,12 @@ export class BriefStore implements PendingSave {
   /** Reveal the masked case BIG-nummer (PRD-0002 §5c). Server re-checks the capability
       + step-up and audits the attempt; on success we swap the masked value in the
       already-loaded caseContext (a field update, not a reload). The step-up gesture
-      itself is the UI's concern — this command just runs the audited server call. */
+      itself is the UI's concern (`behandel-scherm.component.ts`'s `onReveal()` confirm)
+      — this command is only reachable once that gesture has happened, so it is the one
+      that tells the adapter to send `X-Step-Up` (BIO-006a: the adapter itself no longer
+      hardcodes the header). */
   async revealBigNummer() {
-    const r = await this.revealAdapter.reveal();
+    const r = await this.revealAdapter.reveal(true);
     if (!r.ok) {
       this.actionState.set({ tag: 'Failed', error: r.error });
       return;