refactor: apply CLAUDE.md code quality improvements and add packaging

- Add #![forbid(unsafe_code)] to main.rs (issue #3)
- Replace raw ANSI escape codes with owo-colors crate (issue #2)
- Replace manual HOME path construction with dirs::home_dir() (issue #5)
- Ship umutray.service as a static file; service::install() substitutes
  the binary path at install time instead of generating the unit at runtime
- Add packaging/PKGBUILD following Arch Rust package guidelines
- Add CLAUDE.md tracking refactor tasks
- setup.rs: clean up downloaded temp files on abort/back, save launcher
  to config only after successful install, auto-start download when a
  preset has an installer_url
- util.rs: add pick_folder() using zenity/kdialog subprocesses (no rfd)
- config.rs: populate installer_url for all 6 built-in presets with
  official download URLs
- Document the Option<Option<Vec<String>>> gamescope pattern at main.rs:307

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

Cargo.lock

@@ -866,7 +866,7 @@ checksum = "2a76fa97167fa740dcdbfe18e8895601e1bc36525f09b044e00916e717c03a3c"
 dependencies = [
  "dconf_rs",
  "detect-desktop-environment",
- "dirs",
+ "dirs 4.0.0",
  "objc",
  "rust-ini",
  "web-sys",
@@ -945,6 +945,15 @@ dependencies = [
  "dirs-sys 0.3.7",
 ]
 
+[[package]]
+name = "dirs"
+version = "5.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "44c45a9d03d6676652bcb5e724c7e988de1acad23a711b5217ab9cbecbec2225"
+dependencies = [
+ "dirs-sys 0.4.1",
+]
+
 [[package]]
 name = "dirs-sys"
 version = "0.3.7"
@@ -2928,6 +2937,12 @@ dependencies = [
  "ttf-parser 0.25.1",
 ]
 
+[[package]]
+name = "owo-colors"
+version = "4.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d211803b9b6b570f68772237e415a029d5a50c65d382910b879fb19d3271f94d"
+
 [[package]]
 name = "palette"
 version = "0.7.6"
@@ -4407,8 +4422,10 @@ dependencies = [
  "anyhow",
  "clap 4.6.1",
  "directories",
+ "dirs 5.0.1",
  "iced",
  "ksni",
+ "owo-colors",
  "reqwest",
  "serde",
  "serde_json",