chore: import upstream snapshot with attribution

extensions/catalog.json

@@ -0,0 +1,51 @@
+{
+  "schema_version": "1.0",
+  "updated_at": "2026-06-05T00:00:00Z",
+  "catalog_url": "https://raw.githubusercontent.com/github/spec-kit/main/extensions/catalog.json",
+  "extensions": {
+    "agent-context": {
+      "name": "Coding Agent Context",
+      "id": "agent-context",
+      "version": "1.0.0",
+      "description": "Manages coding agent context/instruction files (e.g., CLAUDE.md, copilot-instructions.md) with project-specific plan references and configurable markers",
+      "author": "spec-kit-core",
+      "repository": "https://github.com/github/spec-kit",
+      "bundled": true,
+      "tags": [
+        "agent",
+        "context",
+        "core"
+      ]
+    },
+    "bug": {
+      "name": "Bug Triage Workflow",
+      "id": "bug",
+      "version": "1.0.0",
+      "description": "Assess, fix, and validate bug reports against the codebase with per-bug reports stored under .specify/bugs/<slug>/",
+      "author": "spec-kit-core",
+      "repository": "https://github.com/github/spec-kit",
+      "bundled": true,
+      "tags": [
+        "bug",
+        "triage",
+        "workflow",
+        "qa"
+      ]
+    },
+    "git": {
+      "name": "Git Branching Workflow",
+      "id": "git",
+      "version": "1.0.0",
+      "description": "Feature branch creation, numbering (sequential/timestamp), validation, and Git remote detection",
+      "author": "spec-kit-core",
+      "repository": "https://github.com/github/spec-kit",
+      "bundled": true,
+      "tags": [
+        "git",
+        "branching",
+        "workflow",
+        "core"
+      ]
+    }
+  }
+}