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 Test Vendor 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/lib/types.ts

@@ -27,6 +27,14 @@ export interface Settings {
   renderPrefs: string;
   /** Folder of the last export; kept by the backend (saving settings does not change it). */
   lastExportDir?: string;
+  /** The untouched logo file the derived images came from. */
+  logoOriginalPath: string | null;
+  /** White-ink variant for dark surfaces; only for logos with transparency. */
+  logoKnockoutPath: string | null;
+  /** LogoMeta JSON from the import pipeline; empty until the logo has been through it. */
+  logoMeta: string;
+  /** Whether the logo already contains the business name. Automatic means a wordmark does. */
+  logoIncludesName: "auto" | "yes" | "no";
 }
 
 export interface BankAccount {