feat: add GitHub Activity plugin

[AlexMnrs]

Plugin

• Id: alexmnrs/github-activity
• New plugin
• Update to an existing plugin (version bumped in plugin.toml)

What it does

Adds a native GitHub contribution calendar to the Noctalia bar. The widget
shows today's activity and opens an interactive, theme-aware annual heatmap
with contribution details, streaks, cache status, manual refresh, and a
profile shortcut.

External dependencies

• gh: runs gh api graphql to request the authenticated user's
  contribution calendar from GitHub's GraphQL API. GitHub CLI owns the token;
  the plugin never reads or writes credentials.
• xdg-open: opens https://github.com/<login> from the profile button.

The service stores the latest successful normalized calendar in Noctalia's
per-plugin data directory. It performs no other filesystem writes and does
not download or execute remote code.

Testing

• Tested on Niri
• Tested on Hyprland
• Tested on Sway
• Tested on another compositor:
• Noctalia version tested against: v5.0.0-beta.9-4-g7fd9f7bfa960
• Plugin API level: 24

Validated with python3 .github/workflows/scripts/validate-plugins.py.
Manually verified the bar widget, attached panel, per-cell hover details,
manual refresh, cached-state fallback, and profile launch on Arch Linux with
Hyprland.

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.
• 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

• 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.

[ItsLemmy]

[AlexMnrs]

Updated github-activity/thumbnail.webp in the source repository and this PR.

The new file is the 960×540 WebP exported with the official Noctalia thumbnail generator. The PR branch now contains commit 8a8ddbf; the source repository contains the same asset in commit 09dbd7d.

The plugin manifest validation still passes.

[ItsLemmy]

Thanks. You can probably get away without hardcoding the days and month names, since the plugin API has what you need to format time.