feat(clients): render-scale setting on every client — shared punktfunk_core::render_scale

Client-side supersampling/downscaling: the client asks the host to render
and encode at chosen-resolution × scale (the host does no scaling) and the
presenter rescales the decoded frame to the display. >1 supersamples for
sharpness; <1 lightens the host GPU and the link. Default 1.0 = Native, the
prior behavior.

The geometry lives once in punktfunk_core::render_scale (multiply, preserve
aspect ratio, floor to even, clamp to the codec's per-axis ceiling — 4096
for H.264, 8192 otherwise), the Rust twin of the Apple client's
RenderScale.swift, consumed by the native session client, the presenter's
match-window path, the Windows/Linux settings UIs, Decky, and Android
(settings + host connect + unit test).

Implemented and platform-verified by the Apple-client-features session
(Linux+Android+Apple green there); the punktfunk-core wiring
(pub mod render_scale) is restored here after being lost in a working-tree
reconciliation.

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

clients/session/src/console.rs

@@ -175,6 +175,8 @@ pub fn run(target: Option<&str>) -> u8 {
         // Latched at console start (like the stats tier above): toggling Match window in
         // the console's settings screen applies from the next console launch.
         match_window: crate::session_main::match_window(&settings_at_start),
+        render_scale: settings_at_start.render_scale,
+        render_scale_max_dim: punktfunk_core::render_scale::max_dimension(&settings_at_start.codec),
     };
 
     let result =

clients/session/src/main.rs

@@ -127,6 +127,20 @@ mod session_main {
                 settings.refresh_hz
             },
         };
+        // Render scale: multiply the resolved mode (even + codec-clamped) so the host renders
+        // larger/smaller and the presenter resamples to the window. 1.0 = Native. Applied after the
+        // Native/explicit resolution so it composes uniformly with both.
+        let (sw, sh) = punktfunk_core::render_scale::apply(
+            mode.width,
+            mode.height,
+            settings.render_scale,
+            punktfunk_core::render_scale::max_dimension(&settings.codec),
+        );
+        let mode = Mode {
+            width: sw,
+            height: sh,
+            ..mode
+        };
         SessionParams {
             host: addr,
             port,
@@ -372,6 +386,8 @@ mod session_main {
             overlay: None,
             window_size: window_size(&settings),
             match_window: match_window(&settings),
+            render_scale: settings.render_scale,
+            render_scale_max_dim: punktfunk_core::render_scale::max_dimension(&settings.codec),
         };
 
         let outcome =