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>

src/diagnose.rs

@@ -1,5 +1,6 @@
 use crate::config::{Config, Launcher};
 use anyhow::Result;
+use owo_colors::OwoColorize;
 use std::os::unix::fs::MetadataExt;
 use std::path::Path;
 use std::process::{Command, Stdio};
@@ -50,18 +51,17 @@ pub fn run(config: &Config, name: Option<&str>) -> Result<()> {
         if !c.pass {
             issues += 1;
         }
-        let (sym, col, rst) = if c.pass {
-            ("✓", "\x1b[1;32m", "\x1b[0m")
+        if c.pass {
+            println!("  {} {:24} {}", "✓".green().bold(), c.label, c.detail);
         } else {
-            ("✗", "\x1b[1;31m", "\x1b[0m")
-        };
-        println!("  {col}{sym}{rst} {:24} {}", c.label, c.detail);
+            println!("  {} {:24} {}", "✗".red().bold(), c.label, c.detail);
+        }
     }
     println!();
     if issues == 0 {
-        println!("  \x1b[1;32mAll checks passed.\x1b[0m");
+        println!("  {}", "All checks passed.".green().bold());
     } else {
-        println!("  \x1b[1;31m{issues} issue(s) found — see ✗ items above.\x1b[0m");
+        println!("  {}", format!("{issues} issue(s) found — see ✗ items above.").red().bold());
     }
     println!();
     Ok(())