Orbit documentation: docs, wiki and FAQ pages

docs/overview.md

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+# Overview
+
+**Orbit** is a modern web client for **IRC** — the open chat protocol that has quietly run
+communities for decades. It runs entirely in the browser: pick a nick and you're talking, with
+**no install and no signup**.
+
+It powers [tchatou.fr](https://tchatou.fr/app/), and is built to be **re-pointed at any IRCv3
+network** and **rebranded** from a single `config.json` — without recompiling.
+
+## What makes it different
+
+- **Full IRCv3.** Orbit negotiates 24 capabilities — SASL, message-tags, reactions, typing
+  indicators, read-markers, multi-line messages, server-side history, account registration, and
+  Web Push. See [IRCv3 capabilities](/docs/ircv3/).
+- **Pluggable at runtime.** A static `config.json` is fetched on startup and sets the server,
+  channels, branding, themes and feature flags. One build can serve any community. See
+  [config.json reference](/docs/config/).
+- **Installable PWA.** Mobile-first layout, offline app shell, and notifications when the tab is
+  closed.
+- **Self-hostable.** A static build behind any web server. The project even runs its own git
+  server with [push-to-deploy](/docs/push-to-deploy/).
+- **Free software.** AGPL-3.0 — use it, modify it, self-host it.
+
+## Tech
+
+React 19 · TypeScript · Vite · zustand. Tested with Vitest, linted, and built in CI. The codebase
+is a clean modular tree — see [Architecture](/docs/architecture/).
+
+> New here? Jump to the [Quick start](/docs/quick-start/) to run your own in a minute.