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>

libs/shared/docs/behaviour-spec.mdx

@@ -20,8 +20,8 @@ tested where._
 
 Every bullet below is a real test name from the suite — an `it()` title (frontend) or a test
 method name (backend), read as a sentence. Nothing here is hand-written prose: this page
-**is** the suite, reshaped for a business reader. 404 frontend behaviours across
-8 contexts; 219 backend behaviours across 35 test
+**is** the suite, reshaped for a business reader. 406 frontend behaviours across
+8 contexts; 217 backend behaviours across 36 test
 classes.
 
 ## Frontend (by context)
@@ -541,11 +541,9 @@ classes.
 
 #### registration.policy
 
-- only an active registration within the window is eligible
-- struck-off / suspended registrations are never eligible
+- statusLabel echoes the tag
 - statusColor is total over the union
-- a well-formed status is always consistent
-- a Geregistreerd status without its herregistratieDatum is inconsistent
+- herregistratieDeadline is only set for an active registration
 
 #### submit
 
@@ -768,6 +766,13 @@ classes.
 - keeps unrelated query params and the path/hash
 - is a no-op when neither param is present
 
+#### subjectInterceptor
+
+- stamps X-Subject on an /api/v1/ request once ?subject= has been seen
+- keeps stamping later requests on the same tab after the query param is gone (WP-33-style stickiness)
+- leaves a non-API request untouched even when a subject is known
+- sends no header at all when no subject has ever been seen
+
 #### upload lifecycle messages
 
 - queued → progress → complete
@@ -922,8 +927,6 @@ classes.
 - IntakePolicy returns scholing threshold
 - Registration with duo diploma succeeds
 - Registration with manual diploma is rejected with problem details
-- Zero hours submission is rejected
-- Worked hours submission succeeds
 - Change request with valid phone succeeds
 - Change request with bad phone is rejected
 - Health endpoint is ok
@@ -952,7 +955,6 @@ classes.
 - Not eligible before window
 - Eligible on window boundary
 - Suspended is not eligible
-- Status consistency invariant
 
 ### IdempotencyTests
 
@@ -977,7 +979,6 @@ classes.
 - Punten without gevolgd is rejected
 - Herregistratie is unaffected by the intake only gate
 - Zero uren is still afgewezen not a 400
-- Legacy intakes endpoint enforces it too
 
 ### LetterHtmlTests
 
@@ -1040,6 +1041,11 @@ classes.
 - Rejects a margin outside the allowed range
 - Accepts margins on the boundary
 
+### PhoneFormatContractTests
+
+- A leading plus31 is accepted like the frontends normalised form
+- Parentheses around the area code are accepted like the frontend
+
 ### PreviewEndpointTests
 
 - Preview of an unsent brief renders live with a watermark