Add Battery widget plugin

[Yocraft-2000]

Plugin

• Id: yocraft/battery-widget
• New plugin
• Update to an existing plugin (version bumped in plugin.toml)

What it does

Desktop/Lockscreen widget to show battery.

External dependencies

None.

Testing

• Tested on Niri
• Tested on Hyprland
• Tested on Sway
• Tested on another compositor:
• Noctalia version tested against: v5.0.0
• Plugin API level: 19

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

Plugins run as trusted, unsandboxed Luau in the user's session. Confirm:

• 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.

[Yocraft-2000]

error: battery-widget/README.md: add a short introduction below the title explaining what the plugin does

There is one so idk...

edit: fixed, the description needs at least 8 words

[Yocraft-2000]

Also plugin settings don't hot reload idk if that's something I did wrong or if it's a bug

[ItsLemmy]

1. non-blocking - battery-widget/widget.luau:81

   The refresh path builds a shell string and runs it through noctalia.runAsync:
   "cat " .. path .. batName .. "/capacity " .. path .. batName .. "/status".
   noctalia.runAsync(string) executes via /bin/sh -lc, so batName is interpolated
   into a shell command unescaped. batName comes from the free-form "battery_name"
   string setting when "battery" is set to "custom" (battery-widget/widget.luau:17),
   so shell metacharacters in that value are executed.

   This is user-configures-own-session only, not a remote or cross-user attack
   surface, so it is not a trust blocker. It is still avoidable: the plugin API
   exposes noctalia.readFile, which reads /sys/class/power_supply//capacity
   and /status directly and removes both the shell interpolation and a spawned
   subprocess every refresh interval. If the subprocess is kept, quote and escape
   the value the way battery-graph/battery-desktop.luau:6 does.

2. non-blocking - battery-widget/widget.luau:117

   The chunk defines update() but never renders once at load. The host arms a
   repeating timer whose first fire is one full interval away, and setUpdateInterval
   on battery-widget/widget.luau:1 raises that interval to refresh_interval (default
   60s). Result: after the widget is added, and after every script reload, nothing is
   drawn for up to 60 seconds. Calling refreshBattery() at the end of the chunk fixes
   the cold start.

3. non-blocking - battery-widget/widget.luau:1

   setUpdateInterval (line 1) and getBatName() (line 111) are evaluated once at chunk
   load, unlike layout, show_glyph, show_label, hide_plugged, hide_full, color,
   warning_color and charging_color, which are read inside render()/getColor() and
   therefore track settings live. So "refresh_interval", "battery" and "battery_name"
   only take effect when the chunk is reloaded. This is very likely the "plugin
   settings don't hot reload" behavior reported in the PR conversation. Moving both
   calls inside update() matches what battery-graph/battery-desktop.luau:18 does and
   makes all settings live.