feat: add invite code validity controls

- Add invite code starts/expires fields across contracts, API, Spacetime bindings, and admin UI
- Enforce pending/expired invite code redemption behavior and expose admin status
- Add admin write-operation confirmation guard and documentation
- Add invite code contract/runtime tests

server-rs/crates/spacetime-client/src/runtime.rs

@@ -533,12 +533,16 @@ impl SpacetimeClient {
         admin_user_id: String,
         invite_code: String,
         metadata_json: String,
+        starts_at_micros: Option<i64>,
+        expires_at_micros: Option<i64>,
         updated_at_micros: i64,
     ) -> Result<RuntimeProfileInviteCodeRecord, SpacetimeClientError> {
         let procedure_input = build_runtime_profile_invite_code_admin_upsert_input(
             admin_user_id,
             invite_code,
             metadata_json,
+            starts_at_micros,
+            expires_at_micros,
             updated_at_micros,
         )
         .map_err(|error| SpacetimeClientError::Runtime(error.to_string()))?