fix(icons): replace placeholder Hermes icon with Nous brand artwork

The previous Hermes icon was an inline purple "H" SVG unrelated to the
real Hermes Agent brand. Replace it with the official Nous Research
avatar sourced from hermes-agent/landingpage/icon-512.png, routed
through iconUrls as a Vite URL import. The PNG is post-processed to
strip the 4px black rectangle border (cropped inward by 6px and pasted
back onto a 512x512 transparent canvas). Also switch defaultColor to
black to match the monochrome artwork when the asset falls back to an
initial glyph.

src/icons/extracted/metadata.ts

@@ -273,7 +273,7 @@ export const iconMetadata: Record<string, IconMetadata> = {
     displayName: "Hermes",
     category: "ai-provider",
     keywords: ["hermes", "agent", "nous", "nousresearch"],
-    defaultColor: "#7C3AED",
+    defaultColor: "#000000",
   },
   packycode: {
     name: "packycode",