feat(build): cross-platform desktop packaging; bump to 0.1.0

Adds Docker-based packaging for Linux desktop (deb/rpm), Arch
(.pkg.tar.zst via makepkg), and Windows. Windows cross-compiles from
Linux via the official Tauri path — the x86_64-pc-windows-msvc target
driven by cargo-xwin — and produces an NSIS installer (nsis via
tauri.conf.json targets, since the CLI rejects --bundles nsis on a Linux
host). Verified end to end: builds jellytau.exe + jellytau_x64-setup.exe.

Unifies everything on one registry builder image (Dockerfile.builder):
Android SDK/NDK, rpm/file, clang(+clang-cl)/lld/llvm/nsis, cargo-xwin and
the msvc target. Packaging tools sit in a trailing layer so tool changes
rebuild in ~1min instead of ~15. Desktop stages are thin FROM
${BUILDER_IMAGE} layers; Arch uses a separate archlinux image.

CLAUDE.md: CI must install no system toolchains — everything lives in the
image. Bumps version 0.0.18 -> 0.1.0 (Windows support + webview audio +
equalizer).

TRACES: UR-003, UR-005 | DR-004

scripts/build-arch.sh

@@ -0,0 +1,36 @@
+#!/bin/bash
+# Build an Arch Linux package (.pkg.tar.zst) for JellyTau via makepkg.
+#
+# Tauri's bundler has no pacman target (as of tauri-cli 2.9.x), so we ship a
+# hand-written PKGBUILD in packaging/arch/ and build it with makepkg. This must
+# run on an Arch host / the `arch-build` Docker stage — makepkg is Arch-specific
+# and refuses to run as root, so run it as a non-root user with sudo for deps.
+#
+# Usage (typically inside the arch-build Docker stage as a non-root user):
+#   scripts/build-arch.sh
+#   OUTPUT_DIR=/app/dist scripts/build-arch.sh
+set -euo pipefail
+
+REPO_ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+cd "$REPO_ROOT/packaging/arch"
+
+echo "🏛️  Building JellyTau Arch package"
+echo "=================================="
+
+# Point the PKGBUILD at the working tree and give cargo/bun a writable home.
+export JELLYTAU_SRC="$REPO_ROOT"
+export CARGO_HOME="${CARGO_HOME:-$REPO_ROOT/.cargo-arch}"
+
+# -s installs missing deps (needs sudo/root privileges for pacman), -f overwrites.
+makepkg -sf --noconfirm
+
+echo ""
+echo "✅ Built Arch package(s):"
+ls -1 ./*.pkg.tar.zst
+
+if [[ -n "${OUTPUT_DIR:-}" ]]; then
+  mkdir -p "$OUTPUT_DIR"
+  cp -v ./*.pkg.tar.zst "$OUTPUT_DIR/"
+  echo ""
+  echo "📦 Copied Arch package(s) to $OUTPUT_DIR"
+fi