refactor: move common/shaders/ to src/shaders/

Relocates shared WGSL shaders under src/ where all source code lives,
eliminating the top-level common/ directory.

- Update asset references in workspaces/main/assets.txt and workspaces/test/assets.txt
- Update docs: PROJECT_CONTEXT.md, ARCHITECTURE.md, WORKSPACE_SYSTEM.md, SHADER_REUSE_INVESTIGATION.md

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/src/shaders/render/fullscreen_uv_vs.wgsl b/src/shaders/render/fullscreen_uv_vs.wgsl
new file mode 100644
index 0000000..f9ae427
--- /dev/null
+++ b/src/shaders/render/fullscreen_uv_vs.wgsl
@@ -0,0 +1,15 @@
+// Common vertex shader for fullscreen post-processing effects.
+// Draws a single triangle that covers the entire screen, with uv
+// coordinates in [0..1]
+struct VertexOutput {
+    @builtin(position) position: vec4f,
+    @location(0) uv: vec2f,
+};
+
+@vertex fn vs_main(@builtin(vertex_index) i: u32) -> VertexOutput {
+    let pos = array<vec4f, 3>(vec4f(-1, -1, 0, 1.), vec4f(3, -1, 2., 1.), vec4f(-1, 3, 0, -1));
+    var out: VertexOutput;
+    out.position = vec4f(pos[i].xy, 0.0, 1.0);
+    out.uv = pos[i].zw;
+    return out;
+}