refactor(client): relm4 desktop shell; delete legacy presenter + coverflow (phase 5)

The GTK client becomes a relm4 component tree: AppModel owns the window,
trust gate (rules 1-3), and the spawned session child's lifecycle as
typed messages; the hosts page is a child component with a
FactoryVecDeque of host cards — the HostsCallbacks Rc<dyn Fn> bag, the
busy Cell, and the Rc<RefCell<HostsUi>> cross-page pokes are gone.
Trust/settings/library dialogs stay plain GTK, invoked from update with
a ComponentSender.

Deleted with the in-process presenter: ui_stream.rs, video_gl.rs,
ui_gamepad_library.rs, launch.rs, the khronos-egl dep, and the
PUNKTFUNK_LEGACY_PRESENTER hatch. Every stream (and the console library)
now runs in punktfunk-session; the shell spawns it for card connects and
exec's it for --connect/--browse so the Decky wrapper keeps working. The
request-access flow gains --connect-timeout + a CancelHandle that kills
the child. Screenshot scenes re-pointed onto the components (verified:
hosts + library self-capture; the dialog scenes present correctly and
capture under a GL renderer); the gamepad-library scene is gone with the
page.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/linux-session/src/main.rs

@@ -63,6 +63,17 @@ mod session_main {
         }
     }
 
+    /// The connect budget: 15 s normally; `--connect-timeout SECS` overrides — the
+    /// shell's request-access flow passes ~185 s because the host PARKS the connection
+    /// until the operator clicks Approve.
+    pub(crate) fn connect_timeout() -> Duration {
+        Duration::from_secs(
+            arg_value("--connect-timeout")
+                .and_then(|v| v.parse().ok())
+                .unwrap_or(15),
+        )
+    }
+
     /// One session's pump parameters from the Settings store — shared by `--connect`
     /// and every `--browse` launch. Explicit settings, `0` fields resolved to the
     /// window's display (the GTK client reads the monitor under its window — same
@@ -117,7 +128,7 @@ mod session_main {
             launch,
             pin: Some(pin),
             identity,
-            connect_timeout: Duration::from_secs(15),
+            connect_timeout: connect_timeout(),
             force_software,
         }
     }