feat(helium): switch to the GTK theme with KWin title buttons

Helium now takes its colors from Breeze GTK instead of a generated
theme extension, which reset the GTK theme on every launch.

- Import window_decorations.css from gtk.css so Helium, which doesn't
  load kde-gtk-config's GTK module, draws the KWin title buttons
  instead of Breeze GTK's round ones.
- Add chromium.css to give the compact layout's address bar and
  button segment the title bar color, so the tab strip is one color.
- Disable WaylandWpColorManagerV1 so KWin doesn't lift Helium's dark
  grays (40 -> 44) and the strip matches KDE title bars.
- Drop the Helium theme from build.py and the helium package.

kde/helium/.config/helium-browser-flags.conf

@@ -2,5 +2,7 @@
 --ozone-platform-hint=auto
 --enable-features=AcceleratedVideoDecodeLinuxGL,AcceleratedVideoDecodeLinuxZeroCopyGL,AcceleratedVideoEncoder
 
-# Darwin Breeze theme, generated by kde/theme/build.py
---load-extension=~/.local/share/helium-themes/darwinbreeze
+# Don't tag surfaces as sRGB. KWin shows tagged sRGB through a gamma 2.2
+# curve, which lifts dark grays (40 -> 44), so the tab strip would come out
+# lighter than KDE title bars.
+--disable-features=WaylandWpColorManagerV1

kde/helium/.gitignore

@@ -1,2 +0,0 @@
-# Helium caches the built theme next to the manifest.
-Cached Theme.pak

kde/helium/.local/share/helium-themes/darwinbreeze/manifest.json

@@ -1,100 +0,0 @@
-{
-  "manifest_version": 3,
-  "name": "Darwin Breeze",
-  "version": "1.0",
-  "description": "Generated by kde/theme/build.py from DarwinBreezeDark.colors",
-  "theme": {
-    "colors": {
-      "frame": [
-        35,
-        35,
-        35
-      ],
-      "frame_inactive": [
-        35,
-        35,
-        35
-      ],
-      "frame_incognito": [
-        35,
-        35,
-        35
-      ],
-      "frame_incognito_inactive": [
-        35,
-        35,
-        35
-      ],
-      "toolbar": [
-        35,
-        35,
-        35
-      ],
-      "background_tab": [
-        60,
-        60,
-        60
-      ],
-      "background_tab_inactive": [
-        60,
-        60,
-        60
-      ],
-      "tab_text": [
-        223,
-        223,
-        223
-      ],
-      "tab_background_text": [
-        223,
-        223,
-        223
-      ],
-      "tab_background_text_inactive": [
-        155,
-        155,
-        155
-      ],
-      "toolbar_text": [
-        223,
-        223,
-        223
-      ],
-      "toolbar_button_icon": [
-        223,
-        223,
-        223
-      ],
-      "bookmark_text": [
-        223,
-        223,
-        223
-      ],
-      "omnibox_background": [
-        24,
-        24,
-        24
-      ],
-      "omnibox_text": [
-        222,
-        222,
-        222
-      ],
-      "ntp_background": [
-        24,
-        24,
-        24
-      ],
-      "ntp_text": [
-        222,
-        222,
-        222
-      ],
-      "ntp_link": [
-        63,
-        157,
-        255
-      ]
-    }
-  }
-}

kde/helium/README.md

@@ -1,11 +1,14 @@
 # Helium
 
-Browser flags and the generated Darwin Breeze theme. From the repository root:
+Browser flags for hardware video decoding on Wayland and for colors that
+match KDE apps. From the repository root:
 
 ```sh
 stow -d kde -t "$HOME" helium
 ```
 
-The theme files are included, so the KDE `theme` package does not need to be
-stowed to use Helium's theme. To regenerate its colors from the shared color
-scheme, run `python3 kde/theme/build.py` and restart Helium.
+Helium takes its colors and window buttons from GTK. In Settings →
+Appearance, set Theme to GTK and turn off "Use system title bar and borders".
+With the KDE `theme` package applied, GTK follows the Darwin Breeze colors and
+the window buttons match KWin's; see
+[Darwin Breeze → Helium notes](../theme/README.md#helium-notes).