Add standalone repo scaffolding (README, packaging, CI)

Adds the release/CI machinery bos-settings already has in its own repo:
Forgejo package.yml (tag -> build -> publish to [breadway]) and
mirror.yml (Forgejo -> GitHub). PKGBUILD updated for the flattened
layout and dropped -p breadhelp now that this isn't a workspace member.

packaging/README.md

@@ -0,0 +1,26 @@
+Arch packaging
+==============
+
+`PKGBUILD` builds and installs `breadhelp` from source.
+
+## Local build
+
+```bash
+makepkg -si
+```
+
+## Before publishing to [breadway] repo
+
+1. Tag a release on GitHub.
+2. Update `pkgver` to match the tag.
+3. Update `source` to the release tarball URL.
+4. Run `updpkgsums` (or manually set `sha256sums`).
+
+## Runtime dependencies
+
+| Package | Required | Notes |
+|---------|----------|-------|
+| `gtk4` | yes | UI toolkit |
+| `glib2` | yes | always |
+| `gtk4-layer-shell` | yes | tour overlay (dim mask + spotlight callout) |
+| `snapper` | optional | create-backup one-click fix |