site-theseus-x: fix stale '0.0.9' in Download lede + verify examples

Three references still said 0.0.9 while the meta line, download URLs, and
dl.silentmode.st itself had moved to 0.3.15. Discovered when navigate.st/bns/
theseus.x/ was reported as showing 'Latest is 0.0.9'.

- p.lede 'Latest is <b>0.0.9</b>' → '0.3.15'
- Get-FileHash TheseusNavigator-Setup-0.0.9.exe → -0.3.15.exe
- sha256sum TheseusNavigator-Setup-0.0.9.exe → -0.3.15.exe

Meta line + download <a href>s were already correct at v0.3.15.

Sia mirror bns/theseus/index.html has already been re-uploaded with the
same fix; this commit is so the tree matches what's live.

index.html

@@ -223,7 +223,7 @@
 
 <section id="download">
   <h2>Download</h2>
-  <p class="lede">Latest is <b>0.0.9</b>. Windows installer + portable, and an
+  <p class="lede">Latest is <b>0.3.15</b>. Windows installer + portable, and an
      Android build (Ariadne mobile — same brand, phone form factor).</p>
 
   <div class="plats">
@@ -275,10 +275,10 @@
      <code>releases.silentmode.bch</code> pointer. Three independent surfaces —
      they should all agree.</p>
 <pre>Windows PowerShell:
-  Get-FileHash TheseusNavigator-Setup-0.0.9.exe -Algorithm SHA256
+  Get-FileHash TheseusNavigator-Setup-0.3.15.exe -Algorithm SHA256
 
 macOS / Linux:
-  sha256sum TheseusNavigator-Setup-0.0.9.exe
+  sha256sum TheseusNavigator-Setup-0.3.15.exe
 
 Expected:
   5452a34f211176cf04b7ea77a70fb838f0031b6ea0faed2cd270eae989b20c60</pre>