style: strip to grayscale wireframe

- Remap all non-gray colors (blue, green, red, purple, slate) to gray
  equivalents via Tailwind v4 @theme overrides in layout.css
- Zero out all border-radius values (square everything)
- Zero out all shadow values (no depth)
- Disable all transitions and animations globally
- Change theme-color meta tag from purple (#7B2D8E) to gray (#6b7280)
- Clean up undefined 'underlined' class and typo bg-grey-200

src/routes/login/+page.svelte

@@ -39,7 +39,7 @@
 		{/if}
 		<form
 			onsubmit={handleSubmit}
-			class="bg-grey-200 my-6 flex flex-col items-center justify-center"
+			class="my-6 flex flex-col items-center justify-center"
 		>
 			<p>Login</p>
 			<input type="email" placeholder="Email Address" bind:value={email} required class="my-2" />