docs: cover orbit.modal() and pinned messages

docs/overview.md

@@ -24,6 +24,8 @@ network** and **rebranded** from a single `config.json`, without recompiling.
   closed.
 - **Rich messages.** Image, audio and YouTube links expand inline, and `||spoiler||` text stays
   hidden until you click it.
+- **Pinned messages.** Pin the lines that matter; a per-channel list in the header jumps you
+  straight back to any of them.
 - **Speaks 10 languages.** The UI, system messages, and the bundled plugins are fully translated
   and auto-detected (English, French, German, Spanish, Italian, Turkish, Russian, Nepali, and
   Brazilian + European Portuguese). Pin a default with `defaults.lang`.

docs/plugins.md

@@ -92,6 +92,7 @@ instead. See **[Compiled plugins](https://orbit.tchatou.fr/docs/compiled-plugins
 | `orbit.addShortcut(combo, run)` | register a keyboard shortcut, e.g. `"mod+shift+k"` (mod = Cmd/Ctrl) |
 | `orbit.addTheme(id, {name, vars, css?, icon?, color?})` | register a runtime theme; shows in Settings → Appearance |
 | `orbit.notify(title, body?)` | fire a brand-styled desktop notification (asks permission once) |
+| `orbit.modal(render, {title?, wide?})` | open a modal dialog (core owns the shell); returns a close function |
 | `orbit.h / orbit.html` | render helpers |
 | `log(…)` | namespaced console logger |