feat(ariadne/mobile): 0.17 — the address bar finally searches

Direct answers to the three complaints in one release.

"Doesn't load any results even if I type a keyword" — navigateTo used to
always append .bch to any bare label. So "bitcoin" became
https://bitcoin.bch/ and NXDOMAINed. Now: input with a space, or bare
label with no dot, routes to the user's chosen search engine. Input with
a dot (hello.bch, example.com) stays a URL. Matches Chrome/Firefox
omnibox behaviour exactly.

"Has no check for updates in settings" — new Updates section shows the
installed version + signing-cert SHA-256, with a "Check for updates now"
button that manually polls dl.silentmode.st and toasts the result. If a
newer version exists, the standard silent-prefetch → green-chip → tap-to
-install flow (unchanged from 0.15) kicks in.

"Looks poor compared to a regular browser" — Settings gains three more
sections beyond Resolution / Ariadne's Thread / Maintenance:

- Search: segmented picker for DuckDuckGo (default), Startpage, Brave
  Search, Google, Kagi. Persists via SharedPreferences.
- Updates: version + cert + manual check.
- Privacy: "Clear browsing data" — cookies (CookieManager), form data,
  cache, per-tab history, all in one tap. Bookmarks + tabs preserved.
- About: silentmode.st/theseus + theseus.x links, brand credit.

serveSettingsPage() signature grew to take (indexerOn, searchKey,
currentVersion) so it can render the current selection + version. Added
searchEngineSegment() helper for the picker layout.

Release: ariadne-v0.17.apk sha256
8a655081782ecc17a50a7fcd67c28625ccb0c905cf6b583bdd703a128b2b9b10
Deployed to dl.silentmode.st + silentmode.bch (Sia mirror). Site pages
bumped: silentmode.st/tools + /releases + /theseus + theseus.x.

index.html

@@ -250,12 +250,12 @@
       <h3>Ariadne for Android</h3>
       <p>Phone-sized browser with tap-to-verify provenance — the block and
         transaction behind each name are one tap away.</p>
-      <div class="meta">v0.16 · ~141 KB · self-signed release key · in-app auto-update</div>
+      <div class="meta">v0.17 · ~146 KB · self-signed release key · in-app auto-update</div>
       <div class="btns">
-        <a class="btn acid" href="https://dl.silentmode.st/ariadne-v0.16.apk">Download APK</a>
+        <a class="btn acid" href="https://dl.silentmode.st/ariadne-v0.17.apk">Download APK</a>
       </div>
       <div class="hashes" id="hashes-android">
-        <div class="h"><b>APK</b><code>fa58aa7642319faaa6b23f0f0a46c0adad2ce1f3c5957f4d527ac09241b76574</code></div>
+        <div class="h"><b>APK</b><code>8a655081782ecc17a50a7fcd67c28625ccb0c905cf6b583bdd703a128b2b9b10</code></div>
         <div class="h"><b>Signing key</b><code>46ebbbe5dc73148d66410fd0337b1e6683472128c983e8e2578200b9e3ca548c</code></div>
       </div>
     </div>