Add TDD Extension to community catalog (#3982)

Add tdd extension submitted by @d0whc3r to:
- extensions/catalog.community.json (alphabetical order)
- docs/community/extensions.md community extensions table

Closes #3978

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docs/community/extensions.md

@@ -153,6 +153,7 @@ The following community-contributed extensions are available in [`catalog.commun
 | Superpowers Implementation Bridge | Thin orchestrator between Spec Kit (design) and Superpowers (implementation). Cross-agent. | `process` | Read+Write | [speckit-superpowers-bridge](https://github.com/lihan3238/speckit-superpowers-bridge) |
 | Superspec | Bridges spec-kit with obra/superpowers (brainstorming, TDD, subagent, code-review) into a unified, resumable workflow with graceful degradation and session progress tracking | `process` | Read+Write | [superspec](https://github.com/WangX0111/superspec) |
 | Tasks to GitHub Project | Publish and synchronize Spec Kit tasks as cards on a GitHub Project (v2) kanban board, with priority and status sync between spec.md/tasks.md and the board. | `integration` | Read+Write | [spec-kit-tasks-to-project](https://github.com/mancioshell/spec-kit-tasks-to-project) |
+| TDD Extension | Drives spec-kit implementation with tests: a language-agnostic red-green-refactor loop with a per-feature test list, recorded red and green evidence, and mutation-checked test strength. | `process` | Read+Write | [spec-kit-tdd](https://github.com/d0whc3r/spec-kit-tdd) |
 | Team Assign | Assign tasks.md items to human engineers, split into subtasks, and generate a per-engineer workboard | `process` | Read+Write | [spec-kit-team-assign](https://github.com/tarunkumarbhati/spec-kit-team-assign) |
 | Test Coverage Drift Control | Generate incremental coverage drift reports and planned remediation tasks after implementation | `code` | Read+Write | [spec-kit-test-coverage-drift-control](https://github.com/benizzio/spec-kit-test-coverage-drift-control) |
 | Time Machine | Retroactively apply the full SDD workflow to existing codebases — analyse, spec, and ship feature-by-feature | `process` | Read+Write | [spec-kit-time-machine](https://github.com/teeyo/spec-kit-time-machine) |

extensions/catalog.community.json

@@ -4488,6 +4488,47 @@
       "created_at": "2026-06-22T00:00:00Z",
       "updated_at": "2026-06-22T00:00:00Z"
     },
+    "tdd": {
+      "name": "TDD Extension",
+      "id": "tdd",
+      "description": "Drives spec-kit implementation with tests: a language-agnostic red-green-refactor loop with a per-feature test list, recorded red and green evidence, and mutation-checked test strength.",
+      "author": "d0whc3r",
+      "version": "1.1.2",
+      "download_url": "https://github.com/d0whc3r/spec-kit-tdd/releases/download/v1.1.2/tdd-1.1.2.zip",
+      "repository": "https://github.com/d0whc3r/spec-kit-tdd",
+      "homepage": "https://d0whc3r.github.io/spec-kit-tdd/",
+      "documentation": "https://github.com/d0whc3r/spec-kit-tdd/wiki",
+      "changelog": "https://github.com/d0whc3r/spec-kit-tdd/blob/main/CHANGELOG.md",
+      "license": "MIT",
+      "category": "process",
+      "effect": "read-write",
+      "requires": {
+        "speckit_version": ">=0.11.9"
+      },
+      "provides": {
+        "commands": 4,
+        "hooks": 3
+      },
+      "tags": [
+        "acceptance-tests",
+        "mutation-testing",
+        "property-based-testing",
+        "quality",
+        "red-green-refactor",
+        "spec-kit",
+        "spec-kit-extension",
+        "tdd",
+        "test-driven-development",
+        "test-first",
+        "testing",
+        "unit-tests"
+      ],
+      "verified": false,
+      "downloads": 0,
+      "stars": 0,
+      "created_at": "2026-08-04T00:00:00Z",
+      "updated_at": "2026-08-04T00:00:00Z"
+    },
     "team-assign": {
       "name": "Team Assign",
       "id": "team-assign",