feat(clients/windows): game library page + session window placement + help polish

UX polish batch 2 (plan workstreams D/E5/E6):

- D: a mouse/keyboard game library page over pf-client-core::library (the GTK
  ui_library.rs counterpart): responsive 2-6 column poster grid (2:3 portraits,
  store badge, monogram placeholder while art streams in), loading / error+retry
  / empty / grid states, tap-to-play via a normal spawn carrying --launch id.
  Poster bytes land in a disk cache (%LOCALAPPDATA%\punktfunk\art-cache) so the
  Image widget loads file:/// URIs (reactor has no from-bytes source) and
  revisits render instantly. Reached from a paired host's "Browse library..."
  menu item behind the new "Show game library (experimental)" Settings toggle
  (the shared library_enabled field, Apple/GTK parity). A Shared::library_gen
  generation guard keeps a superseded fetch from publishing (speed-test pattern).

- E5: the session window opens at the shell's own top-left (--window-pos, new
  SessionOpts::window_pos) instead of centered on the primary display - streams
  land on the monitor the shell is on, and the hide/restore handoff reads as one
  window changing content. Fullscreen follows that display.

- E6: the Help shortcuts add Alt+Enter and the controller escape chord
  (LB+RB+Start+Back, hold to disconnect).

Also: rustfmt normalization of the merged probe helper.

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

clients/windows/src/app/connect.rs

@@ -79,6 +79,44 @@ fn initiate_opts(
     }
 }
 
+/// Start a stream that launches a library title on connect (`--launch id`) — the library
+/// page's tap-to-play. The library only opens for paired hosts, so the pin resolves like
+/// a normal initiate; a host forgotten mid-visit routes to the PIN ceremony instead.
+pub(crate) fn initiate_launch(
+    ctx: &Arc<AppCtx>,
+    target: Target,
+    launch: String,
+    set_screen: &AsyncSetState<Screen>,
+    set_status: &AsyncSetState<String>,
+) {
+    *ctx.shared.target.lock().unwrap() = target.clone();
+    let known = KnownHosts::load();
+    let pin = target
+        .fp_hex
+        .as_deref()
+        .and_then(trust::parse_hex32)
+        .or_else(|| {
+            known
+                .find_by_addr(&target.addr, target.port)
+                .and_then(|k| trust::parse_hex32(&k.fp_hex))
+        });
+    let Some(pin) = pin else {
+        set_screen.call(Screen::Pair);
+        return;
+    };
+    connect_with(
+        ctx,
+        &target,
+        Some(pin),
+        set_screen,
+        set_status,
+        ConnectOpts {
+            launch: Some(launch),
+            ..ConnectOpts::default()
+        },
+    );
+}
+
 /// The mode to request: explicit settings, with `0` fields resolved to the native size/refresh
 /// of the display our window is on (mirrors the Linux/Swift clients' native-display default).
 pub(crate) fn resolve_mode(s: &Settings) -> Mode {
@@ -181,6 +219,11 @@ pub(crate) struct ConnectOpts {
     /// failure escalates to the visible "Waking…" wait. The wait's own redial clears the flag,
     /// so it can't loop.
     wake_on_fail: bool,
+    /// A library title id (`steam:570`, …) the host launches during the connect handshake —
+    /// the library page's tap-to-play. Spawn mode passes it as `--launch`; the legacy
+    /// in-process path has no launch plumbing (it predates the library and is slated for
+    /// deletion).
+    launch: Option<String>,
 }
 
 impl Default for ConnectOpts {
@@ -191,6 +234,7 @@ impl Default for ConnectOpts {
             awaiting_approval: false,
             cancel: None,
             wake_on_fail: false,
+            launch: None,
         }
     }
 }
@@ -396,7 +440,7 @@ fn connect_spawn(
         &fp_arg,
         opts.connect_timeout.as_secs(),
         fullscreen,
-        None,
+        opts.launch.as_deref(),
         child,
         move |event| {
             use crate::spawn::SpawnEvent;
@@ -544,7 +588,7 @@ pub(crate) fn request_access(props: &Svc, target: &Target) {
             persist_paired: true,
             awaiting_approval: true,
             cancel: Some(cancel),
-            wake_on_fail: false,
+            ..ConnectOpts::default()
         },
     );
 }