Add event/organisation location with Google Maps links

Events and the organisation profile now have an address, with a
"Directions" link and an embedded Google Maps view (no API key
required) shown on event pages, event cards, and the Contact page.
New events default their location to the org's configured address.

frontend/src/lib/maps.ts

@@ -0,0 +1,9 @@
+/** Opens Google Maps with the address pre-filled — no API key required. */
+export function mapsSearchUrl(address: string): string {
+  return `https://www.google.com/maps/search/?api=1&query=${encodeURIComponent(address)}`;
+}
+
+/** Embeddable Google Maps iframe src for the given address — no API key required. */
+export function mapsEmbedUrl(address: string): string {
+  return `https://maps.google.com/maps?q=${encodeURIComponent(address)}&output=embed`;
+}