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/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 {