feat(deps): vuetify 3→4 (batch 4 phase B, #1449)

Vuetify 4 is a Material-Design-3 styling refresh with revert snippets, not a
component-API overhaul. FC's exposure was small:

- Bump vuetify ^4, vite-plugin-vuetify ^2.1.0, vue ^3.5, engines node>=24.
- Restore the dropped global CSS reset (minimal reset from the upgrade guide) in
  Vuetify's own low-precedence reset layer, so FC's margin-zeroing assumptions hold.
- v-row prop→utility: 'dense' → density=compact (×3), align=center → class=align-center.
- v-snackbar: multi-line removed → min-height=68.
- v-autocomplete #item slot: item→internalItem (item now aliases raw) in TagPicker
  + GalleryFilterBar (item.raw.* → internalItem.raw.*).

ACCEPTED (cosmetic, operator reviews live per plan #158): MD3 typography
(text-body-2 ×73), non-uppercase buttons (v4 dropped the uppercase default),
MD3 elevation. CI verifies BUILD only — the LOOK is the live-review pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/styles/app.css

@@ -39,3 +39,13 @@
    deliberately not used here. `.fc-muted` is a custom class Vuetify never
    emits, so no specificity/reorder fight — no !important needed. */
 .fc-muted { color: rgb(var(--v-theme-on-surface-variant)); }
+
+/* Vuetify 4 dropped its global CSS reset (normalisation moved into each
+   component). FC's layouts assumed the reset zeroed margins on text elements, so
+   restore just that — the "minimal reset" from the v4 upgrade guide — inside
+   Vuetify's own reset layer, which is low precedence so component + app styles
+   still win over it. Batch-4 Vuetify 3→4 (#1449). */
+@layer vuetify-core.reset {
+  ul, ol, figure, details, summary { padding: 0; margin: 0; }
+  h1, h2, h3, h4, h5, h6, p { margin: 0; }
+}