desktop: fix catppuccin-gtk build on python 3.14 / matplotlib 3.11

[patflynn]

Root cause

classic-laddie's system build is broken on main: python3.14-catppuccin-2.5.0 (a dependency of catppuccin-gtk-1.0.3, used for GTK theming in home/desktop.nix) fails its check phase with:

AttributeError: module 'matplotlib.style' has no attribute 'core'

matplotlib 3.11 removed mpl.style.core; catppuccin 2.5.0's matplotlib extra still calls it at import time (upstream issue: catppuccin/python#129, fixed by catppuccin/python#130). This blocks all deploys on classic-laddie (and would break weller/johnny-walker the same way).

Fix

nixpkgs master already fixed this, but the pinned nixos-unstable channel hasn't caught up yet. This PR mirrors the two master commits locally via a nixpkgs.overlays entry in modules/common/desktop.nix:

• 455d916d0c python3Packages.catppuccin: fix build with matplotlib 3.11+ — applies the Fix #129 (caused by matplotlib 3.11 deprecating mpl.style.core) catppuccin/python#130 patch to the python catppuccin library (the actual failing derivation), routed through catppuccin-gtk's python3 argument so nothing else rebuilds.
• 894acc94f6 catppuccin-gtk: fix build with python314+ — patches catppuccin-gtk's sources/build/args.py (argparse type=bool + BooleanOptionalAction is an error on python 3.14), the next failure once the python lib builds.

Both patch files are verbatim copies from those nixpkgs commits. The overlay is temporary: remove it once the nixpkgs pin includes both commits — the daily flake.lock update should bring them within days (a comment in the overlay says the same).

Verification

• nix build .#nixosConfigurations.classic-laddie.config.system.build.toplevel --no-link — full local toplevel build succeeded (note: CI only dry-runs evaluation, so this is stated explicitly here; the patched catppuccin-gtk-1.0.3 built and is in the closure).
• nix flake check — all checks passed.
• klaus _pre-review — no issues found.

Deploy note

After merge, someone needs to run sudo systemctl start cosmo-rebuild once on classic-laddie to bootstrap the auto-rebuild loop (see #613).

Run: 20260712-0926-0fc6e840

[gemini-code-assist]

Code Review

This pull request introduces a temporary Nixpkgs overlay for catppuccin-gtk to resolve build failures caused by Python 3.14 and Matplotlib 3.11 compatibility issues. It adds two patch files to address these problems. However, the patch for Matplotlib 3.11 uses Path without importing it from pathlib, which will result in a runtime NameError when the module is loaded.

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[gemini-code-assist]

The patch uses Path on line 31 (Path(CATPPUCCIN_STYLE_DIRECTORY)), but the import from pathlib import Path is missing from the patched file's imports. In catppuccin 2.5.0, catppuccin/extras/matplotlib.py does not import Path by default. This will cause a NameError: name 'Path' is not defined at runtime when the module is imported.

Please include the from pathlib import Path import in the patch, mirroring the full upstream commit from nixpkgs.

@@ -72,6 +72,8 @@
 import matplotlib as mpl
 import matplotlib.colors
 import matplotlib.style
+from pathlib import Path
+from matplotlib import rc_params_from_file
 
 from catppuccin.palette import PALETTE