arch-updater: add changelog view, fix stuck panel on closed terminal

[Reiling-Jeff]

Plugin

• Id: yuuto/arch-updater

• New plugin
• Update to an existing plugin (version bumped in plugin.toml)

What it does

• Adds a changelog view to the panel: a history-icon button next to Check opens an in-panel "what's new" list, sourced from a new CHANGELOG.md.
• The changelog can open automatically once an update finishes successfully (new Show changelog after updating setting, on by default; never triggers for a rollback or a plain check).
• Fixes: clicking Update in terminal mode now closes the panel right away instead of leaving it open with nothing to show.
• Fixes: closing the terminal window before an update finished used to leave the panel stuck on "Updating in a terminal window…" forever. The engine now writes the run's PID to a small pidfile and polls its liveness (kill -0), so it notices the terminal process is gone (even with no ::EXIT marker) and reports the run as failed, offering the existing retry-in-terminal option. A run legitimately waiting at a PKGBUILD prompt is unaffected.

External dependencies

• cat, kill new: read the terminal run's pidfile and check whether that process is still alive, to detect a closed terminal window. Declared in dependencies in plugin.toml.
• Everything else (pacman/AUR helper/flatpak/pkexec/etc.) is unchanged from the existing plugin.

Testing

• Tested on Niri
• Tested on Hyprland
• Tested on Sway
• Tested on another compositor:
• Noctalia version tested against:
• Plugin API level:

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.
• I created thumbnail.webp with the thumbnail generator.
• 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.

Closes #267