REUSE-WP-0015: dedup owner entries, add report gaps (T02/T03/T05)

Remove 17 owner-migrated capabilities from reuse-surface index (keep
activity-core stub). Add report gaps CLI, roster stats + gaps CI steps.
T01 remains operator-blocked on Gitea publish.

SCOPE.md

@@ -60,6 +60,8 @@ The MVP registry foundation, CLI tooling (REUSE-WP-0003), federation stack
   against `https://reuse.coulomb.social`
 - **Sync local federation manifest from hub** with `reuse-surface hub sync`
 - **Export planning cohorts** with `reuse-surface report cohorts`
+- **Report registry gaps** with `reuse-surface report gaps` (roster blockers,
+  empty scaffolds, dedup stubs)
 - **Bootstrap a sibling registry** with `reuse-surface establish --scaffold`
 - **Verify index publish readiness** with `reuse-surface establish --publish-check`
 - **View registry stats** with `reuse-surface stats` (per-repo or
@@ -101,8 +103,9 @@ See `tools/README.md` for command reference.
 
 - **Status:** active MVP registry with CLI, federation, production hub, and
   workstation-wide registry rollout (REUSE-WP-0014 finished).
-- **Capabilities (reuse-surface):** 20 helix_forge entries in
-  `registry/capabilities/` (18 owner-migrated; dedup pending).
+- **Capabilities (reuse-surface):** 3 helix_forge entries in
+  `registry/capabilities/` (2 meta-registry + 1 `activity-core` stub until
+  publish passes).
 - **Workstation roster:** 60 local git repos at `~/<slug>/` tracked in
   `registry/federation/local-repo-roster.yaml` — all **established**, **60/60**
   hub-registered, **47/60** publish-check pass.