feat(search-backend-selection): Search backend dropdown in Settings

- New features/search-settings: pure view-model (options = available backends
  ∪ 'None (search disabled)', unconfigured entries disabled with a suffix,
  unknown persisted selection prepended, network-seam normalization) + the
  SearchBackendField dropdown (save-on-change, spinner/saved/error states,
  revert-to-persisted on failure, 503 -> disabled field with a 'search not
  available' hint, loading skeleton, help text noting search-mode-only scope).
- store.svelte.ts: searchBackendConfig() / setSearchBackend() over the global
  GET/PUT /search/config routes (503 marked unavailable on the failure variant).
- SettingsPane renders the field under the chat limit; ExtensionsPane lists
  the new module manifest.
- .dispatch mirrors: wire + transport-contract deltas for the new types/routes.

1 files changed, 30 insertions, 0 deletions

diff --git a/.dispatch/wire.reference.md b/.dispatch/wire.reference.md
index 5379b11..6e8daff 100644
--- a/.dispatch/wire.reference.md
+++ b/.dispatch/wire.reference.md
@@ -822,3 +822,33 @@ export interface ComputerEntry extends Computer {
 	readonly usageCount: number;
 }
 ```
+
+---
+
+## 2026-09-24 delta (search-backend-selection — ADDITIVE)
+
+The global search-backend selection wire types (`GET/PUT /search/config`, GLOBAL — not
+workspace-scoped) shipped in `@dispatch/wire` (transport-contract re-exports them):
+
+```ts
+/** The selected backend id. `"none"` = search off (scrape/crawl keep working). */
+export type SearchBackendId = "firecrawl" | "umans" | "none";
+
+/** One dropdown entry; `configured` is the availability gate (umans: UMANS_API_KEY resolves; firecrawl: always). */
+export interface SearchBackendAvailability {
+	readonly id: string;
+	readonly label: string;
+	readonly configured: boolean;
+}
+
+/** Response of `GET /search/config` — the selection + every registered backend's availability. */
+export interface SearchBackendConfigResponse {
+	readonly backend: string;
+	readonly available: readonly SearchBackendAvailability[];
+}
+
+/** Body of `PUT /search/config` — select a backend by id (or `"none"`). */
+export interface UpdateSearchConfigRequest {
+	readonly backend: string;
+}
+```