docs: tag the untagged verifications, and record the UR-007 conflict

Five tests and the schema constant implemented requirements without
carrying a tag, so those requirements read as uncovered when they were
not. No behaviour changes here — every edit is a comment.

Also documents `static` as a real tier rather than an exemption: it is
already in `ci_executable_tiers` and its checks run in CI, and it exists
because DR-007's single binary and DR-012's licence policy are properties
of the build that a unit test could only assert as theatre.

The UR-007 note records a cross-repo status conflict rather than
resolving it. `jRay` JR-025 is `Done` and claims UR-007, but the fetch
path that would exercise it (`jRay` JR-031) is still `Planned`. Either
JR-025 is scoped to selection alone or it over-claims; until that is
settled neither register should be trusted for UR-007 coverage.

The gate reports 0 orphan tags and 19/19 UR coverage.

TRACES: DR-001, DR-014, UR-015, UR-016, UR-018 | SR-003, SR-004

tests/api.rs

@@ -275,6 +275,7 @@ async fn a_pending_manifest_is_not_served() {
     assert_eq!(body["status"], "pending");
 }
 
+/// TRACES: DR-001 | SR-004
 #[tokio::test]
 async fn unknown_field_anywhere_is_rejected_with_400() {
     // §6 stage 2, enforced by `deny_unknown_fields` on every DTO.
@@ -319,6 +320,7 @@ async fn contributor_local_identifiers_are_rejected_not_ignored() {
     assert!(body["message"].as_str().unwrap_or("").contains("jellyfin_id"), "{body}");
 }
 
+/// TRACES: UR-015 | SR-003
 #[tokio::test]
 async fn the_withdrawn_anneal_sec_field_is_rejected() {
     // `anneal_sec` was withdrawn in the SR-003 bump: presence now follows track
@@ -342,6 +344,7 @@ async fn the_withdrawn_anneal_sec_field_is_rejected() {
     );
 }
 
+/// TRACES: UR-015, UR-016 | SR-003
 #[tokio::test]
 async fn the_schema_bump_fields_round_trip() {
     // `extinction_sec` and `gallery_scope` are the SR-003 additions. They are