chore(deps): Tailwind 4 (#5021)

Renovate's tailwindcss bump (PR #150) plus the migration it needs:

- Theme moves from tailwind.config.js into app.css as `@theme inline`,
  mapping the same FabledSword tokens. tailwind.config.js is gone.
- PostCSS runs @tailwindcss/postcss; autoprefixer is dropped, since
  Tailwind 4 prefixes through Lightning CSS.
- Class renames from @tailwindcss/upgrade 4.3.3, reviewed: outline-none
  -> outline-hidden, focus-visible:outline -> outline-solid, shadow ->
  shadow-sm, shadow-sm -> shadow-xs, flex-shrink-0 -> shrink-0. Bare
  `rounded` stays: v4 keeps it at 0.25rem, as before.
- Three v3 preflight defaults kept in a base layer so nothing changes on
  screen: gray-200 default border colour, gray-400 placeholder text and
  the pointer cursor on buttons.
- The unused class-based dark variant is not carried over; no template
  uses `dark:`.

Clears the five high and two moderate npm audit findings that came in
through Tailwind 3 (braces, chokidar, micromatch, fast-glob,
postcss-selector-parser).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/routes/admin/requests/+page.svelte

@@ -291,7 +291,7 @@
     <span class="block text-sm text-text-secondary">Quality profile</span>
     <select
       bind:value={qualityOverride}
-      class="mt-1 w-full rounded-md border border-border bg-background px-3 py-2 text-sm text-text-primary focus:outline-none focus:ring-2 focus:ring-accent"
+      class="mt-1 w-full rounded-md border border-border bg-background px-3 py-2 text-sm text-text-primary focus:outline-hidden focus:ring-2 focus:ring-accent"
     >
       <option value="">Use default</option>
       {#each profiles.data ?? [] as p (p.id)}
@@ -304,7 +304,7 @@
     <span class="block text-sm text-text-secondary">Root folder</span>
     <select
       bind:value={rootOverride}
-      class="mt-1 w-full rounded-md border border-border bg-background px-3 py-2 font-mono text-sm text-text-primary focus:outline-none focus:ring-2 focus:ring-accent"
+      class="mt-1 w-full rounded-md border border-border bg-background px-3 py-2 font-mono text-sm text-text-primary focus:outline-hidden focus:ring-2 focus:ring-accent"
     >
       <option value="">Use default</option>
       {#each folders.data ?? [] as f (f.path)}
@@ -346,7 +346,7 @@
       bind:value={rejectNotes}
       rows="3"
       placeholder="Optional — why this is being set aside"
-      class="mt-1 w-full rounded-md border border-border bg-background px-3 py-2 text-sm text-text-primary placeholder:text-text-muted focus:outline-none focus:ring-2 focus:ring-accent"
+      class="mt-1 w-full rounded-md border border-border bg-background px-3 py-2 text-sm text-text-primary placeholder:text-text-muted focus:outline-hidden focus:ring-2 focus:ring-accent"
     ></textarea>
   </label>
   <div class="mt-5 flex justify-end gap-2">