Rewrite README as public-facing project intro

Replace the default Flutter starter README with an actual
introduction: features, screenshots placeholder, getting-started,
supported platforms, build commands, and tech stack.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -1,17 +1,76 @@
 # Noo
 
-A new Flutter project.
+A fast, native [Nextcloud](https://nextcloud.com) client built with Flutter
+and Material You.
 
-## Getting Started
+Noo gives you a clean, modern way to browse and manage the files on your own
+Nextcloud server — files, photos, shares, activity, and trash, all in one
+app, themed to match your device.
 
-This project is a starting point for a Flutter application.
+## Features
 
-A few resources to get you started if this is your first Flutter project:
+- **Files** — browse, upload, move, rename, delete, and favorite files and
+  folders; sort and filter per folder
+- **Photos** — a dedicated media gallery with a full-screen viewer for images
+  and video
+- **Activity** — a feed of what's changed on your server
+- **Shares** — see and manage what you've shared and what's shared with you
+- **Trash** — restore or permanently delete recently removed items
+- **Material You theming** — dynamic color on supported devices, five
+  built-in accent colors, light/dark/AMOLED
+- **Secure sign-in** — authenticates via Nextcloud's Login Flow v2: you sign
+  in through your browser, and Noo never sees or stores your password,
+  only a scoped app token
 
-- [Learn Flutter](https://docs.flutter.dev/get-started/learn-flutter)
-- [Write your first Flutter app](https://docs.flutter.dev/get-started/codelab)
-- [Flutter learning resources](https://docs.flutter.dev/reference/learning-resources)
+## Screenshots
 
-For help getting started with Flutter development, view the
-[online documentation](https://docs.flutter.dev/), which offers tutorials,
-samples, guidance on mobile development, and a full API reference.
+_Coming soon._
+
+## Getting started
+
+Prerequisites:
+
+- [Flutter](https://docs.flutter.dev/get-started/install) (SDK `^3.12.2`)
+- A Nextcloud server with Login Flow v2 enabled (on by default since
+  Nextcloud 15)
+
+```bash
+flutter pub get
+flutter run
+```
+
+On first launch, enter your server's address — Noo opens your browser to
+finish signing in.
+
+## Supported platforms
+
+Android, iOS, and Windows.
+
+## Building
+
+```bash
+flutter build apk       # Android
+flutter build ios       # iOS
+flutter build windows   # Windows
+```
+
+## Tech stack
+
+Flutter with Material 3, [`provider`](https://pub.dev/packages/provider) for
+state management, and `http`/`dio` talking directly to Nextcloud's WebDAV
+and OCS APIs — no bundled Nextcloud SDK.
+
+## Contributing
+
+Project context for contributors (human or AI) lives in
+[`CLAUDE.md`](CLAUDE.md) and `.claude/context/` — architecture, the server
+integration, styling conventions, and code standards.
+
+```bash
+flutter test      # run tests
+flutter analyze   # static analysis / lints
+```
+
+## License
+
+Not yet licensed for redistribution — license TBD.