chore(evidence): add wave 1 scale-update research evidence

- task-2: fractional-scale-v1 research notes for client surfaces
- task-3: fractional-scale-v1 research notes for layer surfaces + transparency/blur notes

.omo/evidence/task-3-transparency-blur.md

@@ -0,0 +1,11 @@
+## task-3-transparency-blur
+
+### Field added
+- File: include/client.h
+- Line 39: `struct wlr_scene_blur *blur;`
+- Placement: after `struct wlr_scene_shadow *shadow;` (line 38)
+
+### Context
+- Forward declaration not needed — definition provided by `<scenefx/types/wlr_scene.h>` through monitor.h include chain.
+- Field initialized to NULL by ecalloc in createnotify (peachwm.c:1245).
+- No `#include` directives added.