fix #389 review round: settings v3 FOV migration + live apply; AD-90

Dual-lens Opus review of 7e0c1303 (reports committed under
docs/research/). The law, gate, and vertical application are CONFIRMED
at instruction-byte level against the PDB-paired acclient.exe (the BN
text FPU-elides this whole area); the fix round addresses the findings:

- Blast MUST-FIX 1: real schema migration instead of a hand-edited dev
  file. SettingsStore v2->v3: a pre-v3 display.fieldOfView was the
  applied vertical FOV in degrees; v3 means retail's m_fGameFOV.
  LoadDisplay migrates on read - the untouched old default 60 maps to
  the retail default 90; a deliberate other value preserves its visible
  16:9 framing (x (16/9 - 0.1)), clamped to the registered [10,160];
  the next save stamps v3 and migration never reruns. The dev
  settings.json hand-edit was reverted so the migration owns it.
- Blast MUST-FIX 2 / mechanism M2: the Field of View now applies LIVE on
  Save (retail: Render::GRPCallback_OnRenderPreferenceChanged @0x0054d999
  -> SmartBox::SetDefaultFov). RuntimeSettingsTargets gains the camera
  graph and applies through ApplyDisplayWindowState - the update-phase
  seam, deliberately NOT the render-phase preview path (the review's
  WATCH-3 cull-vs-raster landmine).
- Mechanism M1 -> register row AD-90: retail's divisor aspect runs
  through the Render.AspectRatio preference (ComputeAspectForViewport
  @0x0054f150, (w/h) x pref x 0.75) - exactly raw w/h at the registered
  default, which is what acdream assumes; retail's NaN-through-the-gate
  quirk (M3) is folded into the same row as deliberately not reproduced.
- Docs: RetailFieldOfView now cites the decisive vertical proof
  (D3DXMatrixPerspectiveFovLH fovy slot @0x0059ab71), the unconditional
  SmartBox::RenderNormalMode site, and M4's exact horizontal numbers
  (89.0/83.9/80.6 deg); the Config FOV row comment updated to LIVE.
- Blast WATCH 4 disposition: the 15 replay-harness PI/3 constants stay -
  they are CAPTURE-TIME camera parameters for recorded fixtures, not
  production framing; changing them would invalidate the replays.

Tests: +6 SettingsStore migration facts, +1 live-apply fact.
App suite 4,962/3 skips; UI.Abstractions 922.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/AcDream.App.Tests/Rendering/RetailFieldOfViewTests.cs

@@ -29,9 +29,11 @@ public sealed class RetailFieldOfViewTests
     [Fact]
     public void Law_HoldsTheHorizontalViewRoughlyConstant()
     {
-        // The point of the smartbox shape: horizontal FOV stays ~85–90°
-        // across every aspect at the 90° default, instead of ballooning on
-        // wide screens the way a fixed vertical FOV does.
+        // The point of the smartbox shape: horizontal FOV stays within
+        // 80–90° across every aspect at the 90° default (89.0° at 4:3,
+        // 83.9° at 16:9, 80.6° at 21:9 — mechanism review M4's exact
+        // numbers), instead of ballooning on wide screens the way a fixed
+        // vertical FOV does.
         foreach (float aspect in new[] { 4f / 3f, 16f / 9f, 21f / 9f })
         {
             Assert.True(RetailFieldOfView.TryAppliedVerticalFov(