feat(polecat): add core.go with timestamp comment

Add internal/polecat/core.go with a timestamp comment at the top
and a CoreVersion constant for version tracking.

- Generated timestamp: 2026-01-19T05:19:00Z
- CoreVersion: "1.0.0"
- Tests to verify constant exists and has correct value

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: furiosa

internal/polecat/core.go

@@ -0,0 +1,6 @@
+// Generated: 2026-01-19T05:19:00Z
+// Package polecat provides polecat lifecycle management.
+package polecat
+
+// CoreVersion identifies the version of the core polecat module.
+const CoreVersion = "1.0.0"

internal/polecat/core_test.go

@@ -0,0 +1,16 @@
+package polecat
+
+import "testing"
+
+func TestCoreVersion_IsSet(t *testing.T) {
+	if CoreVersion == "" {
+		t.Error("CoreVersion should not be empty")
+	}
+}
+
+func TestCoreVersion_MatchesExpected(t *testing.T) {
+	expected := "1.0.0"
+	if CoreVersion != expected {
+		t.Errorf("CoreVersion = %q, want %q", CoreVersion, expected)
+	}
+}