feat(a2b): first-pass texture render — full-screen event-CG layer

Wire asset resolution into a live Godot render. VM executes set-texture ->
ResourceMap resolves (scene,resId) -> files[section_base+resId] across all
archives -> pre-converted BMP -> composite behind the dialogue. The full-screen
event-CG layer (EV052*) renders end-to-end from the executed bytecode.

- Age.Engine/Sys4/ResourceMap.cs: Resolve + BMP TexturePath; Paths: asset JSONs
- GodotAdvHost: create/set/draw-texture -> TextureRect in a _stage layer
- IHost.DrawTexture + VM dispatch extended with dst x/y (draw-texture args 7/8)
- project.godot 800x600; convert_agf.py all-archive + --scene batch
- engine 8/8, C# --selftest still byte-matches vm0 trace (VM behaviour unchanged)

Known limitations (next chunk = graphics geometry/blend subsystem):
- sprites + BG* via the CG-load subroutine get garbage dst/size — native ops
  stubbed (0x208 get-texture-size + sprite position/anim chain)
- AE* fades draw opaque/instant (no alpha); no chromakey
- slot model approximates the game's immediate-mode blit-onto-slot-0 canvas
- AGF pre-converted to BMP offline (runtime decoder deferred)
See docs/phase-a-slice-plan.md (A2b section).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

engine/Age.Engine/Hosting/CaptureHost.cs

@@ -10,5 +10,5 @@ public sealed class CaptureHost : IHost
     public void WaitForInput() { }
     public void CreateTexture(int slot, int width, int height) { }
     public void SetTexture(long resourceId, int slot) { }
-    public void DrawTexture(int slot, int x, int y, int width, int height) { }
+    public void DrawTexture(int slot, int srcX, int srcY, int width, int height, int dstX, int dstY) { }
 }

engine/Age.Engine/Hosting/IHost.cs

@@ -7,5 +7,5 @@ public interface IHost
     void WaitForInput();
     void CreateTexture(int slot, int width, int height);
     void SetTexture(long resourceId, int slot);
-    void DrawTexture(int slot, int x, int y, int width, int height);
+    void DrawTexture(int slot, int srcX, int srcY, int width, int height, int dstX, int dstY);
 }