Add Forgejo Actions workflows and fix [breadway] repo URL

- .forgejo/workflows/mirror.yml: mirrors every push/tag to GitHub
- .forgejo/workflows/package.yml: builds PKGBUILD on tag and publishes
  bos-settings to the Forgejo Arch package registry (distrib=breadway)
- iso/pacman.conf: replace placeholder repo.breadway.dev with the actual
  Forgejo package registry URL

Requires two Forgejo secrets:
  GITHUB_MIRROR_TOKEN — GitHub PAT with repo push scope
  FORGEJO_TOKEN       — Forgejo token with package:write scope

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.forgejo/workflows/mirror.yml

@@ -0,0 +1,20 @@
+name: Mirror to GitHub
+
+on:
+  push:
+    branches: ['**']
+    tags: ['**']
+
+jobs:
+  mirror:
+    runs-on: [self-hosted, hestia]
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Push to GitHub
+        run: |
+          git remote add github \
+            "https://x-access-token:${{ secrets.GITHUB_MIRROR_TOKEN }}@github.com/Breadway/bos.git"
+          git push github --mirror