launcher-menu: grid of tiles and hicolor icon fallbacks

launcherMenu.grid = { enable; columns; maxRows; } restyles the "+" menu's
programs section as a grid of tiles (icon, name below): Steam's own items
stay in place, maxRows limits the visible rows, and Steam's scroll fade is
recomputed so it only shows where there is more to scroll. The pinned
Desktop row is slim and centred in tile mode.

launcherMenu.iconFallbacks (default utilities-terminal, preferences-system)
installs hicolor copies of Breeze app icons, since Steam resolves program
icons only in hicolor; Konsole and KDE System Settings had none.

The checker gains checkOnly "stylesheet" signatures (matched against the
bundle's CSS files) to cover the scroll fade's gradient; launcher-menu-grid
signatures cover the section keys and the ScrollFade classes.

README.md

@@ -136,6 +136,7 @@ the two files below).
       pinDesktop = "bottom";
       closeOnLaunch = true;
       launchDebounce = 10;
+      grid = { enable = true; columns = 4; maxRows = 4; };
     };
     dashboard = {
       windowMaxScale = 4.0;
@@ -190,6 +191,10 @@ menu list every desktop entry, including terminals such as Konsole.
 | `steamFrame.launcherMenu.pinDesktop` | null or `"top"` / `"bottom"` | `null` | Pin "Desktop" above or below the "+" menu's scrolling list (always visible). `null`: a normal list entry. |
 | `steamFrame.launcherMenu.closeOnLaunch` | bool | `false` | Close the "+" menu as soon as a program in it is clicked. |
 | `steamFrame.launcherMenu.launchDebounce` | unsigned int (seconds) | `0` | Ignore repeated launches of the same program from the "+" menu within this time. `0`: off. |
+| `steamFrame.launcherMenu.grid.enable` | bool | `false` | Show the "+" menu's programs as a grid of tiles (large icon, name below) instead of a list. |
+| `steamFrame.launcherMenu.grid.columns` | int, 1-8 | `4` | Tiles per row (popup is 300 px wide: 3 ≈ 92 px, 4 ≈ 68 px, 5 ≈ 53 px tiles). |
+| `steamFrame.launcherMenu.grid.maxRows` | null or positive int | `null` | Rows visible at once, the rest scrolls. `null`: fill up to the menu's max height (600 px). |
+| `steamFrame.launcherMenu.iconFallbacks` | list of str | `[ "utilities-terminal" "preferences-system" ]` | Icon names installed as hicolor copies of Breeze app icons, so the "+" menu shows them (Konsole, KDE System Settings). `[ ]`: none. Takes effect after a Steam restart. |
 | `steamFrame.dashboard.windowMaxScale` | null or number | `null` | Largest resize-handle scale of SteamVR dashboard windows, relative to their default size. `null`: stock (2). See [Dashboard windows](#dashboard-windows-dashboard). |
 | `steamFrame.dashboard.windowDistance.{world,theater,dashboard}.{min,max}` | null or number (m) | `null` | How close / far grabbed windows can be pulled in / pushed back. `null`: stock (world 0.25-5, theater 1-6, dashboard 0.3-4 m). |
 | `steamFrame.steamvrDebugger.enable` | bool | `true` if a UI patch uses port 8087, else `false` | SteamVR dashboard DevTools on `127.0.0.1:8087` (`VRWebHelper/DebuggerEnabled`), needed by dashboard patches. See [SteamVR debugger](#steamvr-debugger-steamvrdebuggerenable). |
@@ -390,7 +395,10 @@ The signatures are data, in `modules/lib/signatures.json`, shared by the
 patches and the offline checker. Besides `module`/`exports`, an entry can
 list `expects` (strings the patch relies on, e.g. internal property names,
 only checked offline) or be `checkOnly` (anchors a patch uses without the
-finder, e.g. the React prop names of the "+" menu, checked offline only).
+finder, e.g. the React prop names of the "+" menu, checked offline only). A
+`checkOnly` entry with `stylesheet` instead of `module` is matched against
+the bundle's CSS files (`styles` directory of the bundle), e.g. the scroll
+fade's gradient the grid relies on.
 
 For your own patches, `steamFrame.uiPatches.lib.mkPatch` wraps a patch
 written as a function expression with the library, its signatures and
@@ -499,12 +507,62 @@ the program twice.
   ignored and logged (`journalctl --user -u steam-ui-patches`, on the next
   re-injection, i.e. within 15 s). Consequence: a program that exits right
   away can only be started again once the time is up.
+- `grid.enable = true`: the programs section ("Launch Program") becomes a
+  grid of tiles: large icon, name centred below (up to two lines). The
+  "Add desktop window" section stays a list. This only restyles Steam's own
+  items (found through React: the section keyed `programs`), so launching,
+  sounds and the other options above work unchanged; Desktop is a normal
+  tile, or with `pinDesktop` a slim, centred full-width row.
+
+  The popup window is a fixed 300 px wide, so `columns` sets the tile size:
+
+  | `columns` | tile width |
+  |---|---|
+  | 3 | ≈ 92 px |
+  | 4 (default) | ≈ 68 px |
+  | 5 | ≈ 53 px |
+
+  Icons scale with the tile (up to 64 px). `maxRows = n` limits the menu to
+  n rows of tiles (measured, since names take one or two lines); the rest
+  scrolls inside the menu. `null` (default) lets the grid grow up to the
+  menu's stock maximum height (600 px). Steam's scroll fade (the gradient at
+  the top/bottom edge) is shown only where there is more to scroll: Steam
+  computes it only when React re-renders or the list scrolls, so the patch
+  recomputes it after the grid changes the layout.
+
+  Controller navigation keeps working: Steam derives thumbstick / D-pad
+  directions from the panel's CSS grid, so up/down/left/right move between
+  tiles.
 
 All are reverted when the options are turned off (next switch). These
-patches use Steam APIs (`SteamClient.Apps`) and React props rather than
-webpack modules; the offline checker verifies those anchors too.
+patches use Steam APIs (`SteamClient.Apps`), React props and CSS rather
+than webpack modules; the offline checker verifies those anchors too
+(including the scroll fade's class names and stylesheet, checked as a
+`stylesheet` signature against Steam's CSS files).
 Tested with Steam client 1790377368.
 
+#### Icon fallbacks (`launcherMenu.iconFallbacks`)
+
+**Problem:** Steam's scan of host programs resolves a desktop entry's
+`Icon=` name only in the hicolor icon theme (and `pixmaps`), not in the
+desktop's icon theme. Konsole (`Icon=utilities-terminal`) and KDE System
+Settings (`Icon=preferences-system`), which SteamOS ships, have their icons
+only in Breeze, so they show up without an icon in the "+" menu.
+
+**Fix:** for each name in `iconFallbacks` (default: those two), the largest
+Breeze app icon from nixpkgs' `kdePackages.breeze-icons` is installed as
+`~/.nix-profile/share/icons/hicolor/scalable/apps/<name>.svg`
+(`~/.nix-profile/share` is on Steam's `XDG_DATA_DIRS`); desktop entries are
+left alone. Add names for other programs that lack an icon (the `Icon=`
+value of their desktop entry), e.g.
+`iconFallbacks = [ "utilities-terminal" "preferences-system" "system-file-manager" ];`;
+`[ ]` installs nothing. A name Breeze has no app icon for fails the build
+with an error naming it.
+
+**Caveat:** Steam caches the icon lookup (GTK icon cache) for its lifetime,
+and files in the Nix store all have the same 1970 mtime, so new icons show
+up only after Steam is restarted (e.g. a reboot), not on the next switch.
+
 ### Dashboard windows (`dashboard.*`)
 
 **Problem:** SteamVR dashboard windows (Steam, app windows, overlays, the