feat(linux): game library browser; split app.rs into cli/launch/ui_trust

- library.rs + ui_library.rs: the host's unified game library over the
  management API (the Apple LibraryClient/LibraryView ported) — mTLS with the
  paired identity, host verified by its pinned cert fingerprint (ureq + rustls,
  unified with the workspace rustls 0.23); posters load async with monogram
  placeholders, and picking a title starts a session that asks the host to
  launch it (the library id rides the Hello).
- app.rs (~800 lines lighter) splits into cli.rs (argv/headless
  pairing/--connect/screenshot scenes), launch.rs (mode resolve + session
  worker + event stream into the UI) and ui_trust.rs (TOFU / SPAKE2 PIN /
  delegated-approval dialogs); ui_hosts/ui_stream reworked around the split.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

clients/linux/src/main.rs

@@ -10,22 +10,32 @@ mod app;
 #[cfg(target_os = "linux")]
 mod audio;
 #[cfg(target_os = "linux")]
+mod cli;
+#[cfg(target_os = "linux")]
 mod discovery;
 #[cfg(target_os = "linux")]
 mod gamepad;
 #[cfg(target_os = "linux")]
 mod keymap;
 #[cfg(target_os = "linux")]
+mod launch;
+#[cfg(target_os = "linux")]
+mod library;
+#[cfg(target_os = "linux")]
 mod session;
 #[cfg(target_os = "linux")]
 mod trust;
 #[cfg(target_os = "linux")]
 mod ui_hosts;
 #[cfg(target_os = "linux")]
+mod ui_library;
+#[cfg(target_os = "linux")]
 mod ui_settings;
 #[cfg(target_os = "linux")]
 mod ui_stream;
 #[cfg(target_os = "linux")]
+mod ui_trust;
+#[cfg(target_os = "linux")]
 mod video;
 
 #[cfg(target_os = "linux")]