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>

src/AcDream.UI.Abstractions/Panels/Settings/SettingsStore.cs

@@ -20,10 +20,14 @@ public readonly record struct UiWindowPosition(float X, float Y);
 /// <see cref="Input.KeyBindings.LoadOrDefault"/> path.
 ///
 /// <para>
-/// Schema (current version 2):
+/// Schema (current version 3 — v3 changed the MEANING of
+/// <c>display.fieldOfView</c>: it was the applied vertical FOV in degrees,
+/// it is now retail's <c>m_fGameFOV</c> in degrees (#389, the SmartboxFOV
+/// port). <see cref="LoadDisplay"/> migrates pre-v3 values on read — see
+/// <see cref="MigrateLegacyVerticalFovDegrees"/>):
 /// <code>
 /// {
-///   "version": 2,
+///   "version": 3,
 ///   "display": { "resolution": "1920x1080", "fullscreen": false, ... }
 ///   "windowLayouts": { "Character": { "1920x1080": { "chat": { ... } } } }
 /// }
@@ -39,7 +43,7 @@ public readonly record struct UiWindowPosition(float X, float Y);
 /// </summary>
 public sealed class SettingsStore
 {
-    private const int CurrentSchemaVersion = 2;
+    private const int CurrentSchemaVersion = 3;
     private readonly string _path;
 
     public SettingsStore(string path)
@@ -66,11 +70,18 @@ public sealed class SettingsStore
                 return DisplaySettings.Default;
 
             var d = DisplaySettings.Default;
+            // #389 (schema v3): a pre-v3 file's stored fieldOfView was the
+            // applied vertical FOV; the same number now means retail's
+            // gameFOV. Migrate on read — an absent key needs none (it falls
+            // back to the already-v3 default).
+            float fieldOfView = ReadFloat(disp, "fieldOfView", d.FieldOfView);
+            if (ReadSchemaVersion(root) < 3 && disp.TryGetProperty("fieldOfView", out _))
+                fieldOfView = MigrateLegacyVerticalFovDegrees(fieldOfView);
             return new DisplaySettings(
                 Resolution:  ReadString      (disp, "resolution",  d.Resolution),
                 Fullscreen:  ReadBool        (disp, "fullscreen",  d.Fullscreen),
                 VSync:       ReadBool        (disp, "vsync",       d.VSync),
-                FieldOfView: ReadFloat       (disp, "fieldOfView", d.FieldOfView),
+                FieldOfView: fieldOfView,
                 Gamma:       ReadFloat       (disp, "gamma",       d.Gamma),
                 ShowFps:     ReadBool        (disp, "showFps",     d.ShowFps),
                 Quality:     ReadQuality     (disp, "quality",     d.Quality),
@@ -94,6 +105,38 @@ public sealed class SettingsStore
         }
     }
 
+    /// <summary>The file's top-level schema version; a file predating the
+    /// version key reads as 1 (the same convention the v1 radar-layout
+    /// migration below already uses).</summary>
+    private static int ReadSchemaVersion(JsonElement root) =>
+        root.TryGetProperty("version", out var v) && v.ValueKind == JsonValueKind.Number
+            ? v.GetInt32()
+            : 1;
+
+    /// <summary>
+    /// #389 blast-review MUST-FIX 1 — the v3 fieldOfView migration. The
+    /// pre-v3 number was the applied VERTICAL FOV in degrees (written
+    /// straight onto the cameras); the v3 number is retail's
+    /// <c>m_fGameFOV</c> in degrees, run through the smartbox law. Two
+    /// cases:
+    ///  - exactly the old default 60 → the new default 90: 60 was acdream's
+    ///    own invented constant, not a user preference, and mapping it to
+    ///    retail's registered default gives every untouched file the retail
+    ///    experience;
+    ///  - anything else was a DELIBERATE choice → preserve the user's
+    ///    visible framing at the era's default 16:9 aspect:
+    ///    gameFOV = vFOV × (16/9 − 0.1) (the smartbox law inverted at that
+    ///    aspect), clamped into the slider's registered [10,160].
+    /// Runs on READ for any pre-v3 file; the next save stamps version 3 and
+    /// the value stops migrating.
+    /// </summary>
+    internal static float MigrateLegacyVerticalFovDegrees(float legacyVerticalFovDegrees)
+    {
+        if (legacyVerticalFovDegrees == 60f)
+            return 90f;
+        return Math.Clamp(legacyVerticalFovDegrees * (16f / 9f - 0.1f), 10f, 160f);
+    }
+
     /// <summary>
     /// Save Display settings, preserving any other top-level keys the file
     /// already contains (e.g. an <c>audio</c> section written by a newer