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')
+  })
+})