feat(docs): Add Renamify logo to documentation header

- Add SVG logo icon (Lucide replace-all icon)
- Configure logo in Starlight theme header
- Create both standard and large versions of the logo

The logo represents the core functionality of Renamify - replacing all
occurrences of identifiers throughout a codebase.

🤖 Generated with Claude Code

Co-Authored-By: Claude <noreply@anthropic.com>

Author: ndbroadbent

docs/astro.config.mjs

@@ -13,6 +13,9 @@ export default defineConfig({
       title: "Renamify",
       description:
         "Smart search & replace for code and files with case-aware transformations",
+      logo: {
+        src: "./src/assets/logo.svg",
+      },
       editLink: {
         baseUrl: "https://github.com/DocSpring/renamify/edit/main/docs",
       },