feat(branding): optional per-app banner replacing logo + name in header

A brand may ship a wide banner (logo + wordmark in one image) that
replaces the brand-kit logo + app-name pair in a standalone's header.
Events is the first consumer.

Banners are optional and resolve at build time, mirroring the existing
@brand-app-logo chain:

- resolveAppBanner(app?) checks per-standalone override first
  (branding/<dep>/icons/<app>/banner.{svg,png}) then the brand's primary
  banner (branding/<dep>/banner.{svg,png}); returns null when absent
  instead of throwing, so brands without a banner keep logo + name.
- brandAppBannerAliasEntry() always registers the @brand-app-banner
  alias (falling back to the logo) so the static import resolves; whether
  it renders is gated by the VITE_APP_BANNER build flag.
- EventsPage renders the banner when the flag is set, else logo + name.

Deployers override per-standalone without touching the component. SVG
banners must have their text outlined to paths (browsers lack designer
fonts) — documented in branding/README.md.

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

vite-branding.ts

@@ -92,6 +92,46 @@ export function brandAppLogoAliasEntry(app?: string) {
   } as const
 }
 
+/**
+ * Optional brand banner — a wide lockup (logo + wordmark in one image)
+ * that replaces the logo + app-name pair in a standalone's header.
+ *
+ * Resolution mirrors {@link resolveAppLogo} (per-standalone override
+ * first, then the brand's primary banner), but a banner is OPTIONAL:
+ * returns `null` when none is found instead of throwing. Brands that
+ * don't ship a banner keep the default logo + name rendering.
+ */
+export function resolveAppBanner(app?: string): string | null {
+  const candidates: string[] = []
+  if (app) {
+    candidates.push(
+      join(BRAND_DIR, 'icons', app, 'banner.svg'),
+      join(BRAND_DIR, 'icons', app, 'banner.png'),
+    )
+  }
+  candidates.push(
+    join(BRAND_DIR, 'banner.svg'),
+    join(BRAND_DIR, 'banner.png'),
+  )
+  return candidates.find((p) => existsSync(p)) ?? null
+}
+
+/**
+ * Standalone-aware brand-banner alias entry, the banner sibling of
+ * {@link brandAppLogoAliasEntry}. Always registers the
+ * `@brand-app-banner` alias so the static `import '@brand-app-banner?url'`
+ * in the component resolves cleanly — when the active brand has no
+ * banner it falls back to the resolved logo, which the component never
+ * renders (it gates on the `VITE_APP_BANNER` flag instead).
+ */
+export function brandAppBannerAliasEntry(app?: string) {
+  const resolved = resolveAppBanner(app) ?? resolveAppLogo(app)
+  return {
+    find: /^@brand-app-banner(\?.*)?$/,
+    replacement: `${resolved}$1`,
+  } as const
+}
+
 /**
  * PWA manifest name for a standalone. Combines the brand name with the
  * app's own label, or returns the bare brand when no label is given.