Copy the shared house rules into AGENTS.md (#2749)

## Summary
- Puts the shared house-rules blocks at the top of `AGENTS.md`, copied
from craft-contrib `dde09ea31e2e457f5b4653a6e76f7cdf55944bdf`.
- Adds `.github/workflows/house-rules.yml`, which calls the shared
check.

Artcraft is the Tauri product, so it gets the core block only. The Rust
rules are for native Craft apps and shared Rust libraries.
- `CLAUDE.md` was a symlink to `AGENTS.md` and is now `@AGENTS.md`.
- No local paragraph was removed. The Tauri and TypeScript description
stays.

## Sizes
- Core block: 3,052 bytes.
- Root `AGENTS.md`: 6,934 bytes.

.github/workflows/house-rules.yml

@@ -0,0 +1,28 @@
+name: House rules
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - AGENTS.md
+      - CLAUDE.md
+      - .github/workflows/house-rules.yml
+  pull_request:
+    paths:
+      - AGENTS.md
+      - CLAUDE.md
+      - .github/workflows/house-rules.yml
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: house-rules-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  house-rules:
+    uses: storytold/craft-common-actions/.github/workflows/house-rules.yml@main
+    with:
+      rust: false