docs: update README for restyle, Takeout guide, and replacing import

README.md

@@ -6,11 +6,20 @@ already downloaded. Built for the flight.
 
 Tauri 2 · Rust · React · Tailwind CSS 4 · SQLite
 
+Styled to `DESIGN-SYSTEM.md`: slate and sky, a 9–15px type ladder, outline-first
+controls, borders for separation and shadows only for elevation, with light and dark
+both designed rather than one derived from the other.
+
 ## How it works
 
 **Subscriptions come from Google Takeout, not the API.** Export *YouTube subscriptions*
 from [Takeout](https://takeout.google.com/) and import the `subscriptions.csv` in
-Settings. No OAuth, no API key, no Google Cloud project, nothing secret on disk.
+Settings — which carries a seven-step walkthrough with the exact URLs. No OAuth, no API
+key, no Google Cloud project, nothing secret on disk.
+
+Importing **replaces** your subscription list: the CSV becomes the whole truth. Channels
+no longer in it are removed along with their videos and downloaded files. A confirmation
+dialog names exactly what will be deleted before anything happens.
 
 **Video metadata comes from YouTube's public Atom feed** — one request per channel to
 `youtube.com/feeds/videos.xml?channel_id=…`, fetched 8 at a time and merged into a single
@@ -38,15 +47,15 @@ streams that must be merged.
 npm install && npm run tauri dev
 ```
 
-Build a real app bundle:
+Build and install a real app bundle:
 
 ```bash
-npm run tauri build
+npm run tauri build -- --bundles app && cp -R src-tauri/target/release/bundle/macos/FlightTube.app /Applications/
 ```
 
 ## Using it
 
-1. **Settings → Import subscriptions.csv** — point it at your Takeout export.
+1. **Settings** — follow the seven-step Takeout guide, then **Import subscriptions.csv**.
 2. **Refresh** — pulls the latest videos from every channel.
 3. **Download** on any video — progress shows live on the button; click again to cancel.
 4. Click a **downloaded** video to play it in the app. Click an undownloaded one to open
@@ -54,7 +63,8 @@ npm run tauri build
 5. **Offline** — the app detects a lost connection and collapses the feed to your
    downloads. The connectivity pill also toggles a forced offline mode for testing.
 
-Videos land in `~/Movies/FlightTube` (changeable in Settings).
+Videos land in `~/Movies/FlightTube` (changeable in Settings). Appearance follows the
+system by default; Settings offers System / Light / Dark.
 
 ## Limitations
 
@@ -70,9 +80,10 @@ Videos land in `~/Movies/FlightTube` (changeable in Settings).
 cd src-tauri && cargo test
 ```
 
-37 unit tests cover the three places malformed input actually bites: Takeout CSV parsing,
+42 unit tests cover the three places malformed input actually bites: Takeout CSV parsing,
 Atom feed parsing (against a captured real response), and `yt-dlp` progress-line parsing —
-plus the database rule that a refresh must never clobber download state.
+plus the database rules that a refresh must never clobber download state and that a
+replacing import drops exactly the right channels.
 
 Two network-dependent tests are excluded by default:
 
@@ -94,7 +105,9 @@ src-tauri/src/
   commands.rs    Tauri command surface — delegates only
 src/
   components/    Sidebar, TopBar, VideoRow, DownloadButton, Player, Settings
-  hooks/         useFeed, useDownloads, useConnectivity
+  components/ui.tsx        the design system's component vocabulary, in one place
+  components/TakeoutGuide  the seven-step export walkthrough
+  hooks/         useFeed, useDownloads, useConnectivity, useAppearance
 ```
 
 Design notes and the implementation plan are in `docs/superpowers/`.