feat: add command palette, accessibility, scroll animations, and keyboard navigation

Implements COMP-139 (command palette), COMP-140 (accessibility), COMP-141 (scroll animations), COMP-145 (keyboard navigation)

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-Claude)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

apps/web/src/components/repo-input.tsx

@@ -52,10 +52,14 @@ export function RepoInput() {
     <form onSubmit={handleSubmit} className="w-full">
       <div className="relative flex flex-col sm:flex-row gap-3">
         <div className="relative flex-1">
-          <div className="absolute left-4 top-1/2 -translate-y-1/2 text-zinc-500">
+          <label htmlFor="repo-url-input" className="sr-only">
+            GitHub repository URL
+          </label>
+          <div className="absolute left-4 top-1/2 -translate-y-1/2 text-zinc-500" aria-hidden="true">
             <Github className="w-5 h-5" />
           </div>
           <input
+            id="repo-url-input"
             type="text"
             value={url}
             onChange={(e) => {