packaging: add deb/flatpak build flow and desktop metadata

packaging/flatpak/build-flatpak.sh

@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
+MANIFEST="$ROOT_DIR/packaging/flatpak/io.orbithub.OrbitHub.yml"
+DIST_DIR="${1:-$ROOT_DIR/dist/flatpak}"
+BUILD_DIR="$DIST_DIR/build"
+REPO_DIR="$DIST_DIR/repo"
+BUNDLE="$DIST_DIR/io.orbithub.OrbitHub.flatpak"
+
+if ! command -v flatpak-builder >/dev/null 2>&1; then
+  echo "flatpak-builder is required. Install it first:" >&2
+  echo "  sudo apt-get install -y flatpak-builder" >&2
+  exit 1
+fi
+
+mkdir -p "$DIST_DIR"
+
+flatpak-builder \
+  --force-clean \
+  --repo="$REPO_DIR" \
+  "$BUILD_DIR" \
+  "$MANIFEST"
+
+flatpak build-bundle "$REPO_DIR" "$BUNDLE" io.orbithub.OrbitHub
+echo "Created $BUNDLE"