Add a Navara HD renderer choice, release a parked engine after three minutes, and cut Navara's memory

Navara now draws at CSS pixels without MSAA, like Cesium; Navara HD keeps the device pixel ratio and MSAA 4. Only one Navara variant is ever kept. A parked engine is released after three minutes and its WebGL context is lost. Three leaks that kept a released Navara alive are fixed, the canvas context drops its unused antialias buffer, cloud shadows use two 256 px cascades, and the tile cache is budgeted from the screen buffers.

docs/CURRENT-STATE.md

@@ -105,6 +105,24 @@ next to Cesium. It is picked under Display → Globe Engine or with
 `?engine=navara`; Cesium stays the default. Switching is live: the page keeps
 one application, and only the globe-bound parts move to the next engine.
 
+- **Two Navara choices** (`src/app/engineChoice.js`). **Navara** draws at CSS
+  pixels without MSAA, as Cesium does; SMAA still smooths edges. **Navara HD**
+  (`?engine=navara-hd`) draws at the device pixel ratio with MSAA 4. Both are
+  the `navara` engine to the layers; a pick between them builds the other
+  variant cold and releases the first, so only one Navara holds memory.
+  Measured in headless Chrome (Dubai, 1280×800): Navara 1.6 GiB at DPR 1 and
+  1.8 GiB at DPR 2, Navara HD 1.8 and 2.7 GiB, Cesium 0.93 and 1.08 GiB
+  (Navara used 1.95 and 3.0 GiB before).
+- **Memory.** The canvas context has no antialias (Navara draws into its own
+  targets and copies the result), the cloud shadow maps use the low preset's
+  256² and 2 cascades, and the tile cache budget is the screen-sized targets
+  plus 768 MiB instead of Navara's default of up to 2 GiB, which a long session
+  filled. A released Navara keeps no JS: catalog closures capture the
+  operations, not the scene; a released globe aborts with a reason made at
+  module load (a fresh one keeps the stack, and with it the scene); and
+  `Pass.fullscreenGeometry` from postprocessing is disposed after the view,
+  which otherwise pins the canvas through a three listener.
+
 - **The engine contract** is `src/globe/contract.js`. `src/globe/cesium/*` and
   `src/globe/navara/*` implement it, `src/globe/testing/fakeEngine.js` stands
   in for tests, and `src/globe/testing/contractSuite.mjs` runs the same checks
@@ -114,7 +132,11 @@ one application, and only the globe-bound parts move to the next engine.
   camera mode and URL state outlive a switch. A layer that is a session model
   gets `attachRenderer(engine)` / `detachRenderer()` instead of being rebuilt,
   so its data is not fetched again. The outgoing globe is parked
-  (`src/standalone/rendererCache.js`), so switching back is warm.
+  (`src/standalone/rendererCache.js`), so switching back within three minutes
+  is warm (60-90 ms). After that the parked globe is disposed and its WebGL
+  context lost, which frees about 1.1 GiB for a parked Navara; switching back
+  then builds it cold (1.5-2 s). `?parkedMs=` shortens the delay for QA
+  (`scripts/qa-strict-parked-release.mjs`).
 - **Renderers per engine.** Each layer keeps its model and display policy in
   engine-neutral files and draws through `render/cesium*.js` or
   `render/navara*.js`. Cesium renderers are listed in