feat(mirada): mirada-protocol — contrato Cerebro↔Cuerpo del compositor

BrainCommand/BodyEvent + WindowPlacement, marco postcard con prefijo u32
LE (write_frame/read_frame, guard MAX_FRAME) y el puente placements()
desde un Workspace de mirada-layout. 9 tests.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Cargo.lock

@@ -7397,6 +7397,15 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "mirada-protocol"
+version = "0.1.0"
+dependencies = [
+ "mirada-layout",
+ "postcard",
+ "serde",
+]
+
 [[package]]
 name = "moka"
 version = "0.12.15"