fix: set vite base to /build/ so asset paths match the actual serve location

Assets built to public/build/assets/ but index.html referenced /assets/
(no /build/ prefix). Nginx couldn't find them, fell through to Symfony's
catch-all SPA route, which served HTML in place of JS — Vue never loaded.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

public/build/assets/SettingsView-CWIIisVW.css

@@ -0,0 +1 @@
+.settings[data-v-1446e085]{padding:var(--space-4) var(--space-4) calc(64px + var(--space-6));max-width:480px;margin:0 auto}.settings__title[data-v-1446e085]{font-size:var(--text-xl);margin-bottom:var(--space-6);font-weight:700}.settings__section[data-v-1446e085]{margin-bottom:var(--space-6)}.settings__section-title[data-v-1446e085]{font-size:var(--text-sm);color:var(--color-text-muted);text-transform:uppercase;letter-spacing:.06em;margin-bottom:var(--space-3);font-weight:700}.settings__row[data-v-1446e085]{padding:var(--space-3) 0;border-bottom:1px solid var(--color-border);font-size:var(--text-base);justify-content:space-between;align-items:center;display:flex}.settings__row-label[data-v-1446e085]{color:var(--color-text-muted)}.settings__row-value[data-v-1446e085]{font-weight:600}.settings__logout[data-v-1446e085]{min-height:var(--touch-min);padding:var(--space-3) 0;color:var(--color-destructive);font-weight:600;font-size:var(--text-base);align-items:center;text-decoration:none;display:flex}.theme-grid[data-v-1446e085]{gap:var(--space-3);grid-template-columns:repeat(3,1fr);display:grid}.theme-swatch[data-v-1446e085]{align-items:center;gap:var(--space-2);padding:var(--space-3);background:var(--swatch-bg);border-radius:var(--radius-md);cursor:pointer;transition:border-color var(--duration-fast);min-height:var(--touch-min);border:2px solid #0000;flex-direction:column;display:flex;position:relative}.theme-swatch--active[data-v-1446e085]{border-color:var(--swatch-primary)}.theme-swatch__preview[data-v-1446e085]{border-radius:var(--radius-sm);background:var(--swatch-bg);border:1px solid color-mix(in srgb, var(--swatch-text) 15%, transparent);flex-direction:column;justify-content:center;gap:4px;width:100%;height:36px;padding:0 6px;display:flex}.theme-swatch__bar[data-v-1446e085]{background:var(--swatch-primary);border-radius:3px;width:60%;height:6px;display:block}.theme-swatch__dot[data-v-1446e085]{background:var(--swatch-text);opacity:.4;border-radius:2px;width:80%;height:4px;display:block}.theme-swatch__label[data-v-1446e085]{font-size:var(--text-xs);color:var(--color-text);text-align:center;font-weight:600;line-height:1.2}.theme-swatch__check[data-v-1446e085]{top:var(--space-1);right:var(--space-2);font-size:var(--text-sm);color:var(--swatch-primary);font-weight:700;position:absolute}