Add theme-switcher plugin

[theblack-don]

Plugin

• Id: theblackdon/theme-switcher
• New plugin
• Update to an existing plugin (version bumped in plugin.toml)

What it does

A carousel of saved themes. Each theme bundles a palette source (built-in, wallpaper,
community, or custom), the matching palette or generator scheme, one or more wallpapers,
a screenshot path, and a title. Selecting a card applies the palette, wallpaper, and
templates to the shell in one click.

Ships a bar widget (theme-switcher), three shortcuts (open, wallpaper, random),
three panels (carousel, editor, wallpapers), and a wallpaper-ipc service for
keybinding wallpaper switching.

External dependencies

None beyond the shell's own noctalia msg IPC (color-scheme-set, templates-apply,
panel-toggle, screenshot-fullscreen). plugin.toml declares dependencies = [].

Testing

• Tested on Niri
• Tested on Hyprland
• Tested on Sway
• Tested on another compositor: KWin / KineticWE
• Noctalia version tested against: v5.0.1
• Plugin API level: 28

Screenshots / Videos

Checklist

Ready-for-review requirement: Every box in this section must be checked. If any statement is not true, keep the
pull request as Draft. An explanation does not replace a required check.

• The directory name matches the part of id after the / in plugin.toml exactly.
• It ships plugin.toml, README.md, thumbnail.webp, and translations/en.json.
• README.md follows the README template, documents every entry id and dependency, and includes exact panel IPC commands and launcher prefixes where applicable.
• thumbnail.webp is present and relevant; for a new plugin I created it with the thumbnail generator, and for an update I regenerated it with the generator if the visual identity or user-facing appearance changed.
• version follows semver and is bumped in this PR; plugin_api is the oldest API level this plugin requires.
• Every non-English translation in this PR uses a locale supported by Noctalia core, and I can read, write, and understand that language well enough to review and maintain it (no unreviewed machine/LLM translations).
• I did not edit catalog.toml; CI generates it.
• This PR touches exactly one plugin directory.

Code review attestation

Plugins run as trusted, unsandboxed Luau in the user's session. Confirm:
Ready-for-review requirement: Every attestation below must be checked.

• The code is readable and not obfuscated, minified, or generated.
• It does not download and execute remote code.
• Every network call, filesystem write, and spawned process is something the description above accounts for.
• I have the right to publish this code under the license declared in plugin.toml.

[Noctalia-CI]

The description now contains the required template structure.