refactor: move AppContext to presentation crate, structurally enforce boundary

Makefile

@@ -1,9 +1,18 @@
 .DEFAULT_GOAL := check
 
 # Run the full local check suite — same order as CI would.
-check: fmt-check clippy test
+check: fmt-check clippy test check-appcontext
 	@echo "✅ All checks passed"
 
+# Enforce that no application use case imports AppContext (god-object guard).
+check-appcontext:
+	@if grep -rn "AppContext" crates/application/src --include="*.rs" | grep -q .; then \
+	    echo "❌ AppContext found in application crate:"; \
+	    grep -rn "AppContext" crates/application/src --include="*.rs"; \
+	    exit 1; \
+	fi
+	@echo "✅ No AppContext in application crate"
+
 # Apply rustfmt to all files.
 fmt:
 	cargo fmt