fix(integrations): add zed to discovery catalog.json (#3266)

zed is registered, registrar-aligned and registry-tested, but it was the
only one of the 34 integrations absent from integrations/catalog.json,
making it undiscoverable through the discovery manifest. Add the missing
'zed' entry (mirroring the sibling skills entries) and a registry<->catalog
parity regression test so a future integration can't silently drift.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

integrations/catalog.json

@@ -299,6 +299,15 @@
       "author": "spec-kit-core",
       "repository": "https://github.com/github/spec-kit",
       "tags": ["cli", "skills", "z-ai"]
+    },
+    "zed": {
+      "id": "zed",
+      "name": "Zed",
+      "version": "1.0.0",
+      "description": "Zed editor skills-based integration",
+      "author": "spec-kit-core",
+      "repository": "https://github.com/github/spec-kit",
+      "tags": ["ide", "skills"]
     }
   }
 }