Restructure release workflow: dev prepares, Mac builds+uploads

Two scripts:
- prepare-release.sh (run by me/Kiro on dev machine):
  Writes releases/vX.Y.Z.md, bumps packageVersion, commits, tags, pushes

- release.sh (run by you on Mac):
  Reads version from current git tag, reads notes from releases/<tag>.md,
  builds DMG, creates Gitea release, uploads DMG.
  No user input needed — just run ./release.sh

Workflow:
  Dev:  ./prepare-release.sh 1.0.0 'Release notes'
  Mac:  git fetch --tags && git checkout v1.0.0 && ./release.sh

prepare-release.sh

@@ -0,0 +1,68 @@
+#!/bin/bash
+# prepare-release.sh — prepare a release commit and tag (run on dev machine)
+#
+# Usage:
+#   ./prepare-release.sh 1.0.0 "Release notes here..."
+#
+# This script:
+#   1. Writes release notes to releases/v<version>.md
+#   2. Updates packageVersion in build.gradle.kts
+#   3. Commits both
+#   4. Creates and pushes the annotated tag
+#
+# After this, the Mac operator runs ./release.sh to build and upload.
+
+set -euo pipefail
+
+if [ $# -lt 2 ]; then
+    echo "Usage: $0 <version> <release-notes>"
+    echo "  Example: $0 1.0.0 'First release with Android and iPhone support'"
+    exit 1
+fi
+
+VERSION="$1"
+TAG="v${VERSION}"
+NOTES="$2"
+
+# ── Pre-flight ────────────────────────────────────────────────────────────────
+if ! git diff --quiet || ! git diff --cached --quiet; then
+    echo "ERROR: Uncommitted changes. Commit or stash first."
+    exit 1
+fi
+
+if git tag | grep -q "^${TAG}$"; then
+    echo "ERROR: Tag $TAG already exists."
+    exit 1
+fi
+
+# ── Write release notes ───────────────────────────────────────────────────────
+mkdir -p releases
+NOTES_FILE="releases/${TAG}.md"
+cat > "$NOTES_FILE" << EOF
+$NOTES
+EOF
+echo "→ Wrote $NOTES_FILE"
+
+# ── Update version ────────────────────────────────────────────────────────────
+sed -i "s/packageVersion = \"[^\"]*\"/packageVersion = \"${VERSION}\"/" build.gradle.kts
+echo "→ Updated packageVersion to $VERSION"
+
+# ── Commit ────────────────────────────────────────────────────────────────────
+git add "$NOTES_FILE" build.gradle.kts
+git commit -m "Release $TAG"
+echo "→ Committed release files"
+
+# ── Tag ───────────────────────────────────────────────────────────────────────
+git tag -a "$TAG" -m "$NOTES"
+echo "→ Created tag $TAG"
+
+# ── Push ──────────────────────────────────────────────────────────────────────
+echo "→ Pushing to origin..."
+GIT_ASKPASS='' GIT_TERMINAL_PROMPT=0 git push origin HEAD:refs/heads/main 2>&1 || \
+    echo "  (push to main may require running from Mac — tag is local)"
+GIT_ASKPASS='' GIT_TERMINAL_PROMPT=0 git push origin "$TAG" 2>&1 || \
+    echo "  (tag push may require running from Mac)"
+
+echo ""
+echo "✓ Release $TAG prepared."
+echo "  On your Mac: git fetch --tags && git checkout $TAG && ./release.sh"