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/theme/build.py

@@ -4,7 +4,6 @@
 .local/share/color-schemes/DarwinBreezeDark.colors is the only place colors
 are defined. This script derives from it:
 
-  ../helium/.local/share/helium-themes/darwinbreeze/manifest.json
   t3/darwin-breeze.json   (published to T3 Code by apply.sh)
   telegram/DarwinBreezeDark.tdesktop-theme   (not committed; imported into Telegram by hand)
   vscode/   (packed into vscode/darwin-breeze.vsix, installed by apply.sh)
@@ -24,7 +23,6 @@ from pathlib import Path
 HERE = Path(__file__).resolve().parent
 PKG = HERE
 SCHEME = PKG / ".local/share/color-schemes/DarwinBreezeDark.colors"
-HELIUM = PKG.parent / "helium/.local/share/helium-themes/darwinbreeze"
 T3 = HERE / "t3/darwin-breeze.json"
 # Telegram Desktop's built-in night theme, used as the base for every key the
 # scheme has no role for: the colors file from telegramdesktop/tdesktop at
@@ -54,10 +52,6 @@ CYAN = (100, 210, 255)
 # Apple systemYellow; search highlights in T3 Code.
 YELLOW = (255, 255, 0)
 
-# Breeze draws inactive tabs this far from the window color towards the text
-# color (measured in Dolphin: 40 -> 62 with text 222).
-INACTIVE_TAB_MIX = 0.12
-
 
 def load() -> ColorFn:
     cp = configparser.ConfigParser(interpolation=None, strict=False)
@@ -84,7 +78,8 @@ def kwin_compensate(c: Sequence[int]) -> list[int]:
 
     Chromium tags its surfaces as sRGB, KWin shows them with a gamma 2.2
     curve, so dark grays come out lighter (40 -> 44). Encoding the target
-    with the inverse makes Helium land on the same values as native apps.
+    with the inverse makes Chromium apps land on the same values as native
+    apps.
     """
 
     def ch(v: int) -> int:
@@ -95,40 +90,6 @@ def kwin_compensate(c: Sequence[int]) -> list[int]:
     return [ch(v) for v in c]
 
 
-def helium(color: ColorFn) -> dict[str, list[int]]:
-    bar = color("Header", "BackgroundNormal")
-    text = color("Window", "ForegroundNormal")
-    view = color("View", "BackgroundNormal")
-    view_text = color("View", "ForegroundNormal")
-    inactive_tab = mix(bar, text, INACTIVE_TAB_MIX)
-
-    # In Helium's compact layout the active tab and the toolbar segments on
-    # either side share the toolbar color, so toolbar and frame must match
-    # for the strip to read as one bar. Inactive tabs get the lighter Breeze
-    # tab color, the way Dolphin draws them.
-    colors = {
-        "frame": bar,
-        "frame_inactive": bar,
-        "frame_incognito": bar,
-        "frame_incognito_inactive": bar,
-        "toolbar": bar,
-        "background_tab": inactive_tab,
-        "background_tab_inactive": inactive_tab,
-        "tab_text": text,
-        "tab_background_text": text,
-        "tab_background_text_inactive": color("Window", "ForegroundInactive"),
-        "toolbar_text": text,
-        "toolbar_button_icon": text,
-        "bookmark_text": text,
-        "omnibox_background": view,
-        "omnibox_text": view_text,
-        "ntp_background": view,
-        "ntp_text": view_text,
-        "ntp_link": color("View", "ForegroundLink"),
-    }
-    return {k: kwin_compensate(v) for k, v in colors.items()}
-
-
 def ansi(color: ColorFn) -> list[Color]:
     """The 16 colors for the VS Code terminal."""
     bg = color("View", "BackgroundNormal")
@@ -530,7 +491,7 @@ def vscode(color: ColorFn) -> dict[str, str]:
 
     colors = {k: pins.get(k) or recolor(c) for k, c in base.items()}
     colors.update(pins)
-    # Electron is Chromium, so it needs the same KWin compensation as Helium.
+    # Electron is Chromium, so it needs the KWin compensation.
     return {k: hexc(kwin_compensate(c[:3]) + list(c[3:])) for k, c in sorted(colors.items())}
 
 
@@ -638,17 +599,6 @@ def write(path: Path, data: str | bytes) -> bool:
 
 def main() -> None:
     color = load()
-    manifest = {
-        "manifest_version": 3,
-        "name": "Darwin Breeze",
-        "version": "1.0",
-        "description": f"Generated by kde/theme/build.py from {SCHEME.name}",
-        "theme": {"colors": helium(color)},
-    }
-    if write(HELIUM / "manifest.json", json.dumps(manifest, indent=2) + "\n"):
-        # Helium would keep showing the old colors from its cache.
-        (HELIUM / "Cached Theme.pak").unlink(missing_ok=True)
-
     theme = {"version": 1, "name": "Darwin Breeze", "appearance": "dark", "colors": t3(color)}
     write(T3, json.dumps(theme, indent=2) + "\n")