Ship yay, wire up LUKS disk encryption, self-signed Secure Boot, release signing

yay (yay-bin, AUR-only like calamares/bibata) republished to [breadway] via
the same PKGBUILD + Forgejo workflow pattern, so users can reach the wider
AUR beyond bakery's bread ecosystem.

Disk encryption: Calamares' partition module already has LUKS support
enabled by default, but the checkbox led nowhere — no cryptsetup on the
live/target image, no mkinitcpio encrypt hook, no GRUB cryptodisk wiring.
An encrypted install would partition fine and then never boot. Added
cryptsetup, pinned luksGeneration to luks1 (GRUB doesn't support LUKS2 +
Argon2id), and post-install.sh now detects an encrypted root (lsblk TYPE
== crypt) and conditionally adds the encrypt hook + GRUB_ENABLE_CRYPTODISK +
--modules="cryptodisk luks luks2" on both grub-install passes. No effect on
a normal unencrypted install.

Secure Boot: self-signed via sbctl (shipped in packages.x86_64). BOS can't
ship a Microsoft-signed shim without going through Microsoft's own paid
UEFI CA process, so post-install.sh enrolls BOS's own keys automatically
only when the firmware is already in Setup Mode (sbctl status --json),
signs the kernel/bootloader, and leaves it alone otherwise — sbctl's own
pacman hook re-signs on every future kernel/GRUB update, no further
wiring needed.

Release signing: generated a dedicated Ed25519 "BOS Release Signing" key
(not reused from anything else), stored as the GPG_PRIVATE_KEY Forgejo
Actions secret. release-iso.yml now generates SHA256SUMS and a detached
SHA256SUMS.asc signature alongside every ISO upload; public key committed
at KEYS.asc with verification instructions in the README.

README updated: fixed a stale "greetd + tuigreet" line (breadgreet since
round 3), documented yay/encryption/secure-boot/verification.

.forgejo/workflows/yay-bin.yml

@@ -0,0 +1,36 @@
+name: Build and publish yay-bin
+
+# yay (and every AUR helper) is AUR-only — not in Arch's official repos — so
+# BOS maintains an in-house PKGBUILD and publishes the built package to the
+# [breadway] repo, same as bibata-cursor-theme and calamares. Prebuilt
+# release tarball, no build step.
+on:
+  push:
+    paths:
+      - 'packaging/yay-bin/**'
+  workflow_dispatch:
+
+jobs:
+  yay-bin:
+    runs-on: [self-hosted, hestia]
+    container:
+      image: archlinux:latest
+    steps:
+      - name: Build and publish
+        env:
+          PUBLISH_TOKEN: ${{ secrets.REGISTRY_TOKEN }}
+        run: |
+          set -euo pipefail
+          pacman -Syu --noconfirm base-devel git
+          useradd -m builder
+          git config --global --add safe.directory '*'
+          git clone --depth 1 --branch "${GITHUB_REF_NAME}" \
+            "https://git.breadway.dev/${GITHUB_REPOSITORY}.git" /home/builder/src
+          chown -R builder:builder /home/builder/src
+          su builder -c "cd /home/builder/src/packaging/yay-bin && makepkg -f --noconfirm --nocheck"
+          PKG=$(find /home/builder/src/packaging/yay-bin -name '*.pkg.tar.zst' | head -1)
+          curl -fsS -X PUT \
+            -H "Authorization: token ${PUBLISH_TOKEN}" \
+            -H "Content-Type: application/octet-stream" \
+            --data-binary "@${PKG}" \
+            "https://git.breadway.dev/api/packages/Breadway/arch/os"