test(tui): track handoff in the skills-catalog fixture (generation 9)

8fc7869a7 shipped handoff in the bundled starter pack (generation 9) but
left assets/skills-catalog-matrix.json at generation 8, failing
fixture_matrix_covers_exactly_the_shipped_bundle and
model_catalogue_contains_exactly_the_eligible_bundled_skills on every
platform's CI. The fixture is an authored contract; add the handoff entry
(core tier, model+user, in catalogue) and bump the generation.

Verified: cargo test -p codewhale-tui --bin codewhale-tui catalog_matrix — 16 passed, 0 failed (exit=0).

crates/tui/assets/skills-catalog-matrix.json

@@ -15,7 +15,7 @@
     "in_model_catalogue": "true when the skill renders as an ambient catalogue line",
     "shadowed_aliases": "aliases that collide with another canonical bundled name; the canonical skill wins resolution"
   },
-  "generation": "8",
+  "generation": "9",
   "skills": [
     {
       "name": "skill-creator",
@@ -75,6 +75,14 @@
       "in_model_catalogue": false,
       "shadowed_aliases": []
     },
+    {
+      "name": "handoff",
+      "tier": "core",
+      "invocation": "model+user",
+      "aliases": [],
+      "in_model_catalogue": true,
+      "shadowed_aliases": []
+    },
     {
       "name": "best-of-n",
       "tier": "core",