Add frame-controls: move window controls between bar and ⋯ menu by long press

steamFrame.dashboard.frameControls: a long press (longPressMs, default
1.5 s; a ring shows the progress from half of it) on a control under a
dashboard window or on a More Options (three-dot) menu row opens a popup
with "Show in bar", which moves that control between the window's bottom
bar and the menu, for all windows. Placement is keyed by the control's
action icon, kept in the page and its localStorage (survives SteamVR
restarts); inBar / inMenu set defaults. floatInTheater gives theater
windows the Float control back.

The popup is a scene-graph panel of its own, attached to the pressed
button's (or the menu's) anchor like SteamVR's tooltips and menu, so the
bar and menu panels don't change; the menu's focus auto-close is held back
while its popup is open. Coordinates with window-curvature through its
sfui-curv-* contract. Lookups by signature ("frame-controls" in
lib/signatures.json, check-only anchors for the rest).

flake.nix

@@ -23,6 +23,7 @@
       dashboard-windows = ./modules/dashboard-windows.nix;
       steam-close-button = ./modules/steam-close-button.nix;
       window-curvature = ./modules/window-curvature.nix;
+      frame-controls = ./modules/frame-controls.nix;
       # Built with the consumer's pkgs; only the source comes from our input.
       # The key lets the module system deduplicate it when it is imported both
       # directly and through `default`.