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/settings/+page.svelte

@@ -467,7 +467,7 @@
                     {#if (m.breakdown ?? []).length > 0}
                       <button
                         type="button"
-                        class="inline-flex items-center gap-1 rounded outline-none focus-visible:ring-1 focus-visible:ring-accent"
+                        class="inline-flex items-center gap-1 rounded outline-hidden focus-visible:ring-1 focus-visible:ring-accent"
                         aria-expanded={expandedBreakdowns.has(m.key)}
                         onclick={() => toggleBreakdown(m.key)}
                       >
@@ -564,12 +564,12 @@
       <label class="text-sm text-text-secondary" for="profile-displayname">Display name</label>
       <input id="profile-displayname" type="text" maxlength="64"
              bind:value={profileForm.displayName}
-             class="w-full rounded border border-border bg-background px-3 py-2 outline-none focus:border-accent" />
+             class="w-full rounded border border-border bg-background px-3 py-2 outline-hidden focus:border-accent" />
 
       <label class="text-sm text-text-secondary" for="profile-email">Email</label>
       <input id="profile-email" type="email" autocomplete="email"
              bind:value={profileForm.email}
-             class="w-full rounded border border-border bg-background px-3 py-2 outline-none focus:border-accent" />
+             class="w-full rounded border border-border bg-background px-3 py-2 outline-hidden focus:border-accent" />
     </div>
     <button type="button" disabled={profileSaving}
             onclick={onSaveProfile}
@@ -587,18 +587,18 @@
         <input id="password-current" type="password" required minlength="8"
                autocomplete="current-password"
                bind:value={passwordForm.current}
-               class="w-full rounded border border-border bg-background px-3 py-2 outline-none focus:border-accent" />
+               class="w-full rounded border border-border bg-background px-3 py-2 outline-hidden focus:border-accent" />
 
         <label class="text-sm text-text-secondary" for="password-new">New password</label>
         <input id="password-new" type="password" required minlength="8"
                autocomplete="new-password"
                bind:value={passwordForm.new}
-               class="w-full rounded border border-border bg-background px-3 py-2 outline-none focus:border-accent" />
+               class="w-full rounded border border-border bg-background px-3 py-2 outline-hidden focus:border-accent" />
 
         <label class="text-sm text-text-secondary" for="password-confirm">Confirm</label>
         <input id="password-confirm" type="password" required minlength="8"
                bind:value={passwordForm.confirm}
-               class="w-full rounded border border-border bg-background px-3 py-2 outline-none focus:border-accent" />
+               class="w-full rounded border border-border bg-background px-3 py-2 outline-hidden focus:border-accent" />
       </div>
       <button type="submit" disabled={passwordSaving}
               class="rounded bg-accent px-3 py-2 text-sm font-medium text-background disabled:opacity-60">