Add Rust logo pipeline: trim, metrics, knockout and Branding settings

Logos (PNG, JPEG, WebP) are decoded, trimmed to their ink box, downscaled
to 1200 px and re-encoded as a content-addressed print PNG plus a white
knockout variant when the logo has alpha; aspect, ink density, mean colour
and kind (wordmark, mark, tall) are stored with the settings and frozen in
the issue snapshot. Legacy logos are derived at startup. The Arun P logo
PDF shrinks from 334 KB to 92 KB. Settings gains a Branding section with
white and dark previews and a business-name toggle (migration M5).

src/styles/carbon.scss

@@ -396,3 +396,59 @@ body {
   white-space: pre-wrap;
   overflow-wrap: anywhere;
 }
+
+/* ---------- Logo preview (Settings -> Branding) ---------- */
+.voiced-logo-preview {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 1rem;
+}
+
+.voiced-logo-preview__item {
+  margin: 0;
+  width: 14rem;
+}
+
+.voiced-logo-preview__surface {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  box-sizing: border-box;
+  height: 6rem;
+  padding: 1rem;
+  border: 1px solid var(--cds-border-subtle-01);
+  overflow: hidden;
+
+  img {
+    display: block;
+    max-width: 100%;
+    max-height: 4rem;
+    object-fit: contain;
+  }
+}
+
+.voiced-logo-preview__surface--light {
+  background: #ffffff;
+}
+
+.voiced-logo-preview__surface--dark {
+  background: #161616;
+}
+
+.voiced-logo-preview__chip {
+  display: flex;
+  box-sizing: border-box;
+  max-width: 100%;
+  padding: 0.5rem 0.75rem;
+  background: #ffffff;
+  border-radius: 0.5rem;
+
+  img {
+    max-height: 3rem;
+  }
+}
+
+.voiced-logo-preview__item figcaption {
+  margin-top: 0.5rem;
+  font-size: 0.75rem;
+}