feat(places): send a search to Google, once or always

Since 4.3.0 the TREK index and OpenStreetMap answer every search first and
Google is only asked when they find nothing, so a list with the wrong place
on it never reached Google, whatever key the instance had, and the provider
choice only decided who fills the empty case.

Two ways to change that, both only where Google holds the key slot. Under a
result list that did not come from Google, one quiet line sends the same
query to Google Places alone (`provider: 'google'` on the search contract,
the MCP search tool takes it too). And beside the key, an admin switch
"Search with Google only" hands every search and every suggestion to Google
and asks nothing of the index or OpenStreetMap; off by default, read by the
search after the keyed provider so an install without a key, or one on Amap
or OpenStreetMap, is untouched. The panel says so beside the switch.

Both shells share the one rule for when the line is offered (placeSource),
and the wiki names both switches.

client/src/utils/placeSource.test.ts

@@ -0,0 +1,27 @@
+import { describe, expect, it } from 'vitest'
+import { offersGoogleRetry, sourceLabelFor } from './placeSource'
+
+describe('offersGoogleRetry', () => {
+  it('FE-PLACESOURCE-001: offers Google for a list the index or OpenStreetMap answered, only where a key exists', () => {
+    expect(offersGoogleRetry('trek-places+openstreetmap', true)).toBe(true)
+    expect(offersGoogleRetry('openstreetmap', true)).toBe(true)
+    expect(offersGoogleRetry('trek-places+plugin', true)).toBe(true)
+    expect(offersGoogleRetry('trek-places+openstreetmap', false)).toBe(false)
+  })
+
+  it('FE-PLACESOURCE-002: a list Google produced, the offline cache and no list at all have nowhere further to go', () => {
+    expect(offersGoogleRetry('google', true)).toBe(false)
+    expect(offersGoogleRetry('google+plugin', true)).toBe(false)
+    expect(offersGoogleRetry('offline-cache', true)).toBe(false)
+    expect(offersGoogleRetry('', true)).toBe(false)
+  })
+})
+
+describe('sourceLabelFor', () => {
+  it('FE-PLACESOURCE-003: a row names its own index, else the list it came from', () => {
+    const t = (k: string) => k
+    expect(sourceLabelFor({ source: 'openstreetmap' }, 'trek-places+openstreetmap', t)).toBe('OpenStreetMap')
+    expect(sourceLabelFor({}, 'google', t)).toBe('Google')
+    expect(sourceLabelFor({}, 'amap', t)).toBe('places.source.amap')
+  })
+})

client/src/utils/placeSource.ts

@@ -40,6 +40,21 @@ const SOURCE_KEYS: Record<string, string> = {
  * answered the call: Google never marks its places, and a merged list marks only
  * the index side, so an unmarked row in one is OpenStreetMap by elimination.
  */
+/**
+ * Whether a result list can be sent to Google instead.
+ *
+ * The index and OpenStreetMap answer first, and Google is only asked when they
+ * find nothing, so a list that has the wrong place on it never reaches Google
+ * on its own. The link that sends it there is offered when the instance has a
+ * Google key and this list did not already come from Google: a list Google
+ * produced, alone or as the empty-case fallback, has nowhere further to go, and
+ * the offline cache is not a search at all.
+ */
+export function offersGoogleRetry(listSource: string, hasMapsKey: boolean): boolean {
+  if (!hasMapsKey || !listSource) return false
+  return !listSource.split('+').includes('google') && listSource !== 'offline-cache'
+}
+
 export function sourceLabelFor(place: unknown, listSource: string, t: TranslationFn): string | null {
   const own = (place as { source?: unknown } | null)?.source
   const source = typeof own === 'string' && own