fix(street-level): /revmain cleanup after the slim rebuild

- Google 3D: the OPEN button re-measures a ground whose tiles are still
  loading (a few times, a second apart) and on a map change, not only
  after the next camera move.
- Mapillary: two mounts on one host during the first download share one
  build instead of leaking a second WebGL viewer.
- Retired floating-panel keys (v8 panelPos, panelFloatHintShown) are
  dropped from localStorage; dead inline-position resets, the drag JSDoc
  and the dead qa-ui-disposal observer branch are gone.
- Docs: z ladder, panel chrome, position storage and the fixture gate's
  actual coverage; changelog fragment for #974 (old .gev-cache/mapillary
  can be deleted).
- ru/es: the layer is named as everywhere else in the UI.
- Fixtures and test fakes: unused exports removed; a fake credit removal
  of an absent credit no longer drops another one; the tile test reset
  frees upstream slots.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/layers/streetLevel/selection.test.mjs

@@ -180,6 +180,19 @@ test('Esc in a text field or rich-text editor keeps the selection (M61)', () =>
   }
 });
 
+test('a click on the position marker neither selects nor opens at the ground', () => {
+  const h = harness();
+  try {
+    h.scene.under = 'sl:pos';
+    h.click();
+    assert.deepEqual(h.groundClicks, []);
+    assert.deepEqual(h.opened, []);
+    assert.deepEqual(h.sequences.selects, []);
+  } finally {
+    h.restore();
+  }
+});
+
 test('a click on nothing of ours goes to the ground handler with the pick, which decides', () => {
   const h = harness();
   try {