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>

Cargo.lock

@@ -1146,6 +1146,9 @@ name = "fastrand"
 version = "2.4.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9f1f227452a390804cdb637b74a86990f2a7d7ba4b7d5693aac9b4dd6defd8d6"
+dependencies = [
+ "getrandom 0.3.4",
+]
 
 [[package]]
 name = "fec-rs"
@@ -1233,6 +1236,7 @@ version = "0.12.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5e139bc46ca777eb5efaf62df0ab8cc5fd400866427e56c68b22e414e53bd3be"
 dependencies = [
+ "fastrand",
  "futures-core",
  "futures-sink",
  "spin",
@@ -1259,6 +1263,15 @@ dependencies = [
  "percent-encoding",
 ]
 
+[[package]]
+name = "fragile"
+version = "2.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8878864ba14bb86e818a412bfd6f18f9eabd4ec0f008a28e8f7eb61db532fcf9"
+dependencies = [
+ "futures-core",
+]
+
 [[package]]
 name = "fs-err"
 version = "3.3.0"
@@ -2995,10 +3008,10 @@ dependencies = [
  "anyhow",
  "async-channel",
  "gtk4",
- "khronos-egl",
  "libadwaita",
  "pf-client-core",
  "punktfunk-core",
+ "relm4",
  "serde_json",
  "tracing",
  "tracing-subscriber",
@@ -3445,6 +3458,41 @@ dependencies = [
  "tokio",
 ]
 
+[[package]]
+name = "relm4"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6420f090f0545e9ec9656469d139a4e1b66ff9c30b808fe2247892724f71a198"
+dependencies = [
+ "flume",
+ "fragile",
+ "futures",
+ "gtk4",
+ "libadwaita",
+ "once_cell",
+ "relm4-css",
+ "relm4-macros",
+ "tokio",
+ "tracing",
+]
+
+[[package]]
+name = "relm4-css"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f3b81d263f784b103c815afa29124486b59741eca069ce7a5999efb14f13c368"
+
+[[package]]
+name = "relm4-macros"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "36c9dbf50a60c82375e66b61d522c936b187a11b25c0a42e91c516326ad24a4f"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "ring"
 version = "0.17.14"