fix(status): stop false LOAD FAILED from a relayed adsb.lol 429 and the installations zoom prompt

Two independent triggers turned the global status chip red while every layer
was still populated (reproduced at JFK in Cockpit; timeline in the issue).

adsb.lol proxy: a non-OK upstream status was relayed verbatim even with a
12 s-old cache in hand, and the browser layer answers a 429 with a 45 s
cooldown in which every refresh reports "adsb.lol rate limited" without a
network call. The proxy now serves its cached body as STALE on a 429/5xx and
backs off from upstream for Retry-After (bounded), mirroring the OpenSky
proxy. A failure with nothing cached is still relayed.

Mapped installations: the "zoom in" guidance was stored in `error`, so the
manager reported a refresh failure and the chip a LOAD FAILED whenever the
view could not be bounded (Cockpit looks at the horizon). The status is now
set without an error string; the row reads the prompt from `statusMessage`,
and the chip ignores `error` for guidance statuses, matching the carve-out
layerFeedState already has.

src/data/militaryInstallations.test.mjs

@@ -758,6 +758,8 @@ test('zoom-out aborts an active installation request and returns non-loading gui
     assert.equal(observedSignal.aborted, true);
     assert.equal(militaryInstallationsLayer.getStats().loading, false);
     assert.equal(militaryInstallationsLayer.getStats().status, 'zoom-in');
+    assert.equal(militaryInstallationsLayer.getStats().error, null, 'guidance is not a fault');
+    assert.match(militaryInstallationsLayer.getStats().statusMessage, /zoom in/i);
   } finally {
     militaryInstallationsLayer.destroy(viewer);
     globalThis.fetch = originalFetch;