feat(client): the overlay learns absorb + clear, so per-control shells can edit profiles too

Groundwork for the Windows half of P1, and a dedup of the Linux one.

The two shells commit differently: GTK writes once when the dialog closes (so it can hand
over a list of touched rows), WinUI writes on every control change (so it can't). `absorb`
serves the second shape — give it the effective settings before and after one control
fired, and it records the field that moved.

That is deliberately NOT the diff-on-save the design rejects. The comparison is against
the EFFECTIVE settings, i.e. what the control was actually showing, not against the
globals — so setting a value back to whatever the global happens to be still records an
override, which is exactly the pin the design wants. It only ever adds; removing an
override stays an explicit, separate operation.

`clear` is that operation, keyed by the overlay's own field names, with `resolution` as
the one alias for the width/height/match-window tri-state a single control drives on every
client. The GTK reset path now calls it instead of carrying its own `match` — that second
list was already a place where the two could drift, and the next client would have made it
a third.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

clients/linux/src/ui_settings.rs

@@ -400,30 +400,12 @@ fn commit_profile(
         o.fullscreen_on_stream = Some(values.fullscreen_on_stream);
     }
     // Resets last: a row the user reset may also have fired its change handler on the way
-    // (a ComboRow re-seeds), and "back to inheriting" is the later, explicit intent.
+    // (a ComboRow re-seeds), and "back to inheriting" is the later, explicit intent. The field
+    // names are the overlay's own, so the list of what can be cleared lives in ONE place —
+    // this used to be a second `match` here, which is exactly how the two drift.
     for key in cleared {
-        match *key {
-            "resolution" => {
-                o.match_window = None;
-                o.width = None;
-                o.height = None;
-            }
-            "refresh_hz" => o.refresh_hz = None,
-            "render_scale" => o.render_scale = None,
-            "bitrate_kbps" => o.bitrate_kbps = None,
-            "codec" => o.codec = None,
-            "hdr_enabled" => o.hdr_enabled = None,
-            "compositor" => o.compositor = None,
-            "audio_channels" => o.audio_channels = None,
-            "mic_enabled" => o.mic_enabled = None,
-            "touch_mode" => o.touch_mode = None,
-            "mouse_mode" => o.mouse_mode = None,
-            "invert_scroll" => o.invert_scroll = None,
-            "inhibit_shortcuts" => o.inhibit_shortcuts = None,
-            "gamepad" => o.gamepad = None,
-            "stats_verbosity" => o.stats_verbosity = None,
-            "fullscreen_on_stream" => o.fullscreen_on_stream = None,
-            other => tracing::warn!(field = other, "reset of an unknown overlay field"),
+        if !o.clear(key) {
+            tracing::warn!(field = key, "reset of an unknown overlay field");
         }
     }
     if let Err(e) = catalog.save() {