scaffold tasks extension

Empty skeleton mirroring the events extension layout: config/manifest,
pyproject + Makefile + ruff/mypy config, FastAPI routers wired into
tasks_ext, NostrClient bootstrap stubs, and an empty static/routes.json.

Models, migrations, CRUD, Nostr publisher/sync, and the API/template
layers land in follow-up commits.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

manifest.json

@@ -0,0 +1,9 @@
+{
+  "repos": [
+    {
+      "id": "tasks",
+      "organisation": "aiolabs",
+      "repository": "tasks"
+    }
+  ]
+}