Add proposal application fixtures

internal/framework/proposals/doc.go

@@ -0,0 +1,7 @@
+// Package proposals provides deterministic, literal proposal preview and
+// application helpers for transcript rewriting.
+//
+// The package only enforces structural and replacement-safety rules.
+// It does not perform semantic validation; LLM-backed and deterministic
+// validators are layered later in the pipeline.
+package proposals