Add GitHub templates and CI workflow

- PR template
- Issue templates (bug report, feature request)
- Hassfest validation workflow

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.github/workflows/validate.yaml

@@ -0,0 +1,17 @@
+name: Validate
+
+on:
+  push:
+  pull_request:
+  schedule:
+    - cron: "0 0 * * *"
+  workflow_dispatch:
+
+jobs:
+  hassfest:
+    name: Hassfest
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: home-assistant/actions/hassfest@master
+        if: github.server_url == 'https://github.com'