feat(server): scan library on startup by default + README first-run walkthrough

Make a fresh install usable out of the box and document the first-run flow
for the public-facing repo.

- Default scan_on_startup to true (Default() + config.example.yaml, which is
  the live config baked into the image). Previously false, so a fresh stack
  came up with an empty library and no hint to scan. Scans are incremental
  (mtime skip), so the per-restart cost is just a directory walk. Re-point
  the env-override test to exercise the override against the new default.
- README: add a "First run" walkthrough (register -> scan -> integrations ->
  install Android app -> invite users), each grounded in a real route.
- Add docs/screenshots/ with six captures, referenced via width-constrained
  <img> wrapped in a link (shrink inline + click to open full size).
  API token and invite token were cropped/redacted out of the captures
  before commit so no live credential lands in the public history.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -4,7 +4,7 @@ A self-hosted music server that thinks for you. Smart shuffle, contextual likes,
 
 > State and intelligence belong on the server, not the client.
 
-<!-- TODO: screenshot of the home page -->
+<a href="docs/screenshots/home.png"><img src="docs/screenshots/home.png" width="820" alt="Minstrel home — your library at a glance"></a>
 
 ## Highlights
 
@@ -58,7 +58,29 @@ volumes:
 docker compose up -d
 ```
 
-After the stack is up, visit `http://localhost:4533/register` and create your admin account. The first user to register on a fresh instance is automatically marked as the administrator; subsequent users can register through the same form (or via invite tokens generated from the admin Users panel, depending on how you configure registration).
+## First run
+
+With the stack up, a handful of in-app steps get you to a working library. Use your own host in place of `localhost` if you're reaching the server over a LAN/VPN address (plain `http://` is fine — no TLS required).
+
+**1. Create your admin account.** Visit `http://localhost:4533/register`. The first account on a fresh instance is automatically the administrator; later users join through the same form or an invite token (step 5).
+
+<a href="docs/screenshots/register.png"><img src="docs/screenshots/register.png" width="320" alt="Creating the first (admin) account on a fresh instance"></a>
+
+**2. Let the first library scan finish.** `scan_on_startup` is on by default, so Minstrel walks your mounted library on boot and imports artists, albums, and tracks — no button to press. Watch progress (and re-scan any time) on the **Admin** page (`/admin`); the scan runs in stages and is incremental, so later restarts only pick up what changed.
+
+<a href="docs/screenshots/library-scan.png"><img src="docs/screenshots/library-scan.png" width="820" alt="The Admin page, where the library scan runs and reports progress"></a>
+
+**3. (Optional) Name the instance and wire up integrations.** In admin **Settings → Integrations** (`/admin/integrations`), add a ListenBrainz token (scrobbling + similarity radio) and/or a Lidarr URL + API key (the request flow). These live in the UI and apply without a restart; the display name can also be set via `MINSTREL_BRANDING_APP_NAME`.
+
+<a href="docs/screenshots/integrations.png"><img src="docs/screenshots/integrations.png" width="820" alt="ListenBrainz and Lidarr integration cards in admin Settings"></a>
+
+**4. Install the Android app.** Open **Settings** (`/settings`) and use the *Install the Android app* card to download the APK that ships inside this server image, then sign in with the same account. From then on the app self-updates straight from your server.
+
+<a href="docs/screenshots/android-download.png"><img src="docs/screenshots/android-download.png" width="820" alt="The &quot;Install the Android app&quot; download card in Settings"></a>
+
+**5. Invite the rest of the household.** From admin **Users** (`/admin/users`), generate an invite token (or enable open registration). Each person gets their own account, so likes, play history, and recommendations stay per-user.
+
+<a href="docs/screenshots/invite-users.png"><img src="docs/screenshots/invite-users.png" width="820" alt="Generating an invite token in admin Users"></a>
 
 For the full configuration surface, see [`config.example.yaml`](./config.example.yaml).