feat(niri-displays): add per-output enable/disable toggle

[jrohland]

Plugin

• Id: raycursive/niri-displays
• New plugin
• Update to an existing plugin (version bumped in plugin.toml)

What it does

Adds a per-output Enabled toggle to each display card, so an output can be
switched off and back on without leaving Noctalia. It runs Niri's existing
temporary output IPC:

niri msg output <port> off
niri msg output <port> on

The last enabled output is protected — its toggle is locked and relabelled
"Only display", so a session can never be left without a screen. A disabled
output keeps its card and stays togglable, while its mode, refresh-rate,
rotation and scale controls remain greyed out.

This also fixes a latent draft bug the feature exposes: a disabled output
reports 0,0 geometry, and syncFromState only seeded positionDraft when it
was nil, so re-enabling a display left the layout editor's Apply pointing at
0,0. Drafts are now reset on the disabled → enabled transition.

No service change was needed: normalizeOutputs already derives enabled from
the JSON, and disabled outputs stay listed by niri msg outputs with
"current_mode": null, "logical": null.

External dependencies

None beyond the existing niri dependency already declared in plugin.toml.
The only new command is niri msg output <port> on|off, shell-quoted through
the plugin's existing quoteShellArgument and dispatched via the existing
runNiri wrapper.

Testing

Tested against a live 3-output Niri session (DP-1 5120x1440, DP-7 1920x1080,
eDP-1 disabled), with the plugin loaded from a local path plugin source.

• Verified niri msg output eDP-1 on / off round-trips, with
  niri msg --json outputs showing logical flipping between non-null and
  null.

• Opened the panel and confirmed the Enabled toggle renders and reflects state
  for both enabled and disabled outputs, and that a disabled output's other
  controls stay greyed while its toggle stays live.

• Dumped the service snapshot via
  noctalia msg plugin raycursive/niri-displays:displays all dump and confirmed
  enabled is correct per output.

• Ran the repo validator (.github/workflows/scripts/validate-plugins.py) —
  clean.

• Tested on Niri

• Tested on Hyprland

• Tested on Sway

• Tested on another compositor:

• Noctalia version tested against: v5.0.1

• Plugin API level: 9

Screenshots / Videos

Checklist

• 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

• 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]

CC @raycursive: this pull request was automatically moved to draft until you have had a chance to look at it. It will be marked ready for review automatically once you reply here.