Cut the Google requests the HUD summary makes on its own

The HUD builds place context for its AI summary whenever the camera
settles, and each build paid for up to four reverse geocodes plus a Nearby
Places search, even when no OpenAI key was configured to use them.

- Ask GET /api/openai/hud-summary/status once; with no summary configured,
  or after an unconfigured reply, make no place lookups for the page.
- Reverse-geocode at most two points: the view center and one viewport
  point.
- Reuse a lookup until the view center moves a quarter of the visible
  width, the camera's distance to it doubles or halves, or the camera
  crosses a lookup height. The reused points are asked again, so only a
  timeout, failure or empty answer spends.
- Repaint the last AI reply when a small pan leaves the context unchanged.

Cached-only hosts and voice context lookups are unchanged.

docs/CURRENT-STATE.md

@@ -4,6 +4,24 @@ Docker Compose mounts the checkout with the shared SELinux `:z` label so
 containers can read it on enforcing SELinux hosts. The separate image-owned
 `node_modules` volume and loopback-only port publishing remain unchanged.
 
+The HUD's AI summary line looks up place names for the view only when the
+summary can use them. The page asks `GET /api/openai/hud-summary/status` once;
+a server without an OpenAI key answers `{ configured: false }`, and the HUD then
+makes no reverse-geocode or Nearby Places request until the page reloads. A
+server without the route is asked once, and an unconfigured summary reply
+stops the lookups the same way. Each lookup reverse-geocodes at most two
+points: the view center alone below 10 km, the center and one viewport point
+up to 750 km, and two viewport points up to 3000 km; Nearby Places is still
+added below 25 km. A lookup is reused until the view center moves a quarter of
+the visible width, the camera's distance to the center doubles or halves, or
+the camera crosses one of those heights. The width is measured from the
+camera's distance to the view center, so terrain and tilt scale it. A reused
+lookup asks again only for what it did not get (a timeout, a failure, an empty
+answer); everything else is a cache hit. A small pan over a reused lookup
+repaints the last AI reply instead of asking for a new one. A host passing
+`cachedOnly` keeps reading every cached sample. Voice context lookups are
+unchanged.
+
 The HUD's LAT/LON degrees-minutes-seconds readout rounds the coordinate once, to
 hundredths of a second, and then splits it. A value within 0.005" of the next
 whole minute carries into the minutes and degrees, so `-122.35` reads