feat(app): render landblock with height-ramp shader + orbit camera

Adds a 2-stage GLSL shader (vertex + fragment), a Shader helper that
compiles/links and exposes SetMatrix4 for uniforms, and an OrbitCamera
with yaw/pitch/distance and a 192-unit-centered target for a single
landblock. TerrainRenderer now takes a Shader and issues an actual
DrawElements call with uView + uProjection uniforms. GameWindow owns
the Shader and Camera, routes mouse drag to camera yaw/pitch, and
scroll wheel to camera distance.

The fragment shader maps world Z to a green-brown-white ramp so
lowlands read green, midlands brown, and peaks white — no textures
yet, but enough to visually confirm the terrain shape.

Shaders are copied to the output dir via a <None Update> item group.

Smoke verified against real dats: process stays alive with no GL
errors, no shader compile/link failures, and no exception trail.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/Shaders/terrain.frag

@@ -0,0 +1,14 @@
+#version 430 core
+in float vHeight;
+out vec4 fragColor;
+
+void main() {
+    float t = clamp(vHeight / 200.0, 0.0, 1.0);
+    vec3 low  = vec3(0.10, 0.35, 0.15);  // green lowland
+    vec3 mid  = vec3(0.55, 0.45, 0.25);  // brown mid
+    vec3 high = vec3(0.90, 0.90, 0.95);  // snowy peak
+    vec3 color = t < 0.5
+        ? mix(low, mid, t * 2.0)
+        : mix(mid, high, (t - 0.5) * 2.0);
+    fragColor = vec4(color, 1.0);
+}

src/AcDream.App/Rendering/Shaders/terrain.vert

@@ -0,0 +1,14 @@
+#version 430 core
+layout(location = 0) in vec3 aPos;
+layout(location = 1) in vec3 aNormal;
+layout(location = 2) in vec2 aTex;
+
+uniform mat4 uView;
+uniform mat4 uProjection;
+
+out float vHeight;
+
+void main() {
+    vHeight = aPos.z;
+    gl_Position = uProjection * uView * vec4(aPos, 1.0);
+}