chore(pkg): add Arch Linux PKGBUILDs for game client and sync server

- pkg/solitaire-quest/PKGBUILD: builds solitaire_app binary, depends on
  alsa-lib, libxkbcommon, systemd-libs (Bevy Linux requirements); check()
  runs only non-Bevy crates (solitaire_core, solitaire_sync) since Bevy
  integration tests require a GPU/display unavailable in chroot
- pkg/solitaire-quest-server/PKGBUILD: builds solitaire_server binary,
  installs systemd service unit and hardened environment file template
- pkg/solitaire-quest-server/solitaire-quest-server.service: systemd unit
  with ProtectSystem=strict, NoNewPrivileges, dedicated service user
- pkg/solitaire-quest-server/server.env: documented env template installed
  to /etc/solitaire-quest-server/server.env (mode 0640, listed in backup=)
- LICENSE: add MIT license
- Cargo.toml: add license = "MIT" to [workspace.package]
- All member crates: add license.workspace = true

Both PKGBUILDs follow the Arch Rust package guidelines:
  prepare() uses --locked + cargo fetch
  build() uses --frozen --release -p <crate>
  RUSTUP_TOOLCHAIN=stable and CARGO_TARGET_DIR=target set in each stage

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

pkg/solitaire-quest-server/server.env

@@ -0,0 +1,15 @@
+# Solitaire Quest Server — environment configuration
+# This file is installed to /etc/solitaire-quest-server/server.env (mode 0640).
+# Edit these values before starting the service.
+
+# Path to the SQLite database file.
+# The directory must be writable by the solitaire-quest service user.
+DATABASE_URL=sqlite:///var/lib/solitaire-quest-server/solitaire.db
+
+# HS256 signing secret for JWT tokens.
+# Generate a strong secret with: openssl rand -hex 32
+# REQUIRED — server will refuse to start if unset.
+JWT_SECRET=changeme_generate_with_openssl_rand_hex_32
+
+# TCP port the server listens on.
+SERVER_PORT=8080