style(web): official 'Powered by Flux' lockup across app + landing

Replace the plain-text 'Powered by RunOnFlux' badges (web app Header/Footer and
the landing header/footer) with the official Flux lockup SVG, matching the mobile
app for consistent branding. Two art variants (dark art on light bg, light art on
dark) are swapped via the existing theme system (prefers-color-scheme +
:root[data-theme]). Links to runonflux.com.

Author: TheTrunk

clients/web/landing/index.html

@@ -64,6 +64,19 @@
   .top .right { display: flex; align-items: center; gap: 14px; }
   .badge-flux { font-family: var(--mono); font-size: 11px; color: var(--ink-3); border: 1px solid var(--line);
     padding: 4px 9px; border-radius: 20px; white-space: nowrap; }
+  /* Official "Powered by Flux" lockup — two art variants swapped by theme. */
+  .pbf { display: inline-flex; align-items: center; line-height: 0; opacity: 0.92; }
+  .pbf:hover { opacity: 1; }
+  .pbf img { width: auto; display: none; }
+  .pbf .pbf-on-light { display: inline; }
+  @media (prefers-color-scheme: dark) {
+    .pbf .pbf-on-light { display: none; }
+    .pbf .pbf-on-dark { display: inline; }
+  }
+  :root[data-theme="light"] .pbf .pbf-on-light { display: inline; }
+  :root[data-theme="light"] .pbf .pbf-on-dark { display: none; }
+  :root[data-theme="dark"] .pbf .pbf-on-light { display: none; }
+  :root[data-theme="dark"] .pbf .pbf-on-dark { display: inline; }
   .theme-btn { background: transparent; border: 1px solid var(--line); color: var(--ink-2); border-radius: 20px;
     width: 34px; height: 34px; cursor: pointer; display: inline-flex; align-items: center; justify-content: center;
     font-size: 15px; line-height: 1; }
@@ -244,7 +257,10 @@
     <a href="#apps">Get the app</a><a href="#trust">Privacy</a>
   </nav>
   <div class="right">
-    <span class="badge-flux">Powered by RunOnFlux</span>
+    <a class="pbf" href="https://runonflux.com" target="_blank" rel="noreferrer" aria-label="Powered by Flux — opens runonflux.com">
+      <img class="pbf-on-light" src="/powered_by_dark.svg" alt="Powered by Flux" height="16" />
+      <img class="pbf-on-dark" src="/powered_by_light.svg" alt="" height="16" aria-hidden="true" />
+    </a>
     <button class="theme-btn" id="themeToggle" type="button" aria-label="Toggle light / dark theme" title="Toggle theme">◐</button>
   </div>
 </div></header>
@@ -499,7 +515,7 @@ <h4>Learn</h4>
     </div>
     <div class="col">
       <h4>Network</h4>
-      <a href="https://runonflux.io">Powered by RunOnFlux</a>
+      <a href="https://runonflux.com">Powered by Flux</a>
       <a href="https://home.runonflux.io">Flux dashboard</a>
     </div>
   </div>