fix(plugins): install plugin packages from a .zip (#896)

Root cause: Install Plugin from Disk only opened a folder picker and the host could only copy folders, so a zipped plugin could not be installed. The picker now accepts a .zip or a package's plugin.toml, and the host's install_from_path unpacks a zip to a temporary folder and runs it through the existing install_from_dir validation. The package may sit at the archive root or in its only folder (archiver metadata such as __MACOSX is ignored). Archives with unsafe paths or symbolic links, more than 10,000 entries or over 1 GB unpacked are refused, and a zip without plugin.toml (e.g. an IntelliJ plugin) gets a clear error.

Fixes #892

Co-authored-by: florentvdry <[email protected]>

docs/plugins/themes.md

@@ -109,8 +109,8 @@ There is no build step. The package *is* the folder.
 1. Copy `templates/theme-plugin` and rename `id`, `name` and the theme files.
 2. Edit the colours. Keep `kind` truthful (`light` for light backgrounds).
 3. **Install:** *Settings › Plugins › ⚙ › Install Plugin from Disk…* (or the
-   *Install Plugin from Disk…* action) and pick the package folder. The
-   manifest and the files it references are copied to
+   *Install Plugin from Disk…* action) and pick the package's `plugin.toml`, or
+   a `.zip` of the folder. The manifest and the files it references are copied to
    `<app-data>/plugins/<id>/`.
 4. **Apply:** in *Settings › Plugins*, select the plugin and press *Apply* next
    to the theme. *Use Default Theme* switches back.