legal: addlicense headers + normalize legacy variants (Phase 0 RED-4)

Phase 0 closure (Path B2, post-rewrite):

addlicense sweep — adds the canonical certctl LLC copyright + BUSL-1.1
SPDX header to every production Go file. Template:

  // Copyright 2026 certctl LLC. All rights reserved.
  // SPDX-License-Identifier: BUSL-1.1

Coverage: 338 / 338 production Go files (cmd/ + internal/, excluding
*_test.go and **/testdata/**). Pre-sweep coverage was 22 / 338 (6.5%);
post-sweep is 338 / 338 (100%).

Normalized 22 pre-existing legacy headers (`// Copyright (c) certctl`
+ `// SPDX-License-Identifier: BSL-1.1`) and 1 file using a
`Certctl Contributors` attribution. The legacy SPDX ID `BSL-1.1`
is non-standard; the official SPDX identifier for Business Source
License 1.1 is `BUSL-1.1` (capital U). All 338 files now share the
canonical form.

Generated via:
  addlicense -c "certctl LLC" -y 2026 \
    -f cowork/legal/copyright-header.tpl \
    -ignore '**/testdata/**' -ignore '**/*_test.go' \
    cmd/ internal/

Verification:
  find cmd internal -name '*.go' -not -name '*_test.go' \
    -not -path '*/testdata/*' \
    -exec grep -L '^// Copyright 2026 certctl LLC' {} \; | wc -l

  Returns: 0

gofmt clean. Header additions are comments only, no compile impact.

Closes: cowork/certctl-architecture-diligence-audit.html#fix-RED-4

internal/pkcs7/certrep.go

@@ -1,3 +1,6 @@
+// Copyright 2026 certctl LLC. All rights reserved.
+// SPDX-License-Identifier: BUSL-1.1
+
 // CertRep PKIMessage response builder for SCEP.
 //
 // RFC 8894 §3.3.2 (Certificate Response Message Format) +

internal/pkcs7/envelopeddata.go

@@ -1,3 +1,6 @@
+// Copyright 2026 certctl LLC. All rights reserved.
+// SPDX-License-Identifier: BUSL-1.1
+
 // EnvelopedData parser + decryptor for SCEP PKIMessage.
 //
 // RFC 5652 §6 (Cryptographic Message Syntax — EnvelopedData) +

internal/pkcs7/envelopeddata_builder.go

@@ -1,3 +1,6 @@
+// Copyright 2026 certctl LLC. All rights reserved.
+// SPDX-License-Identifier: BUSL-1.1
+
 // EnvelopedData BUILDER (inverse of envelopeddata.go's parser+decryptor).
 //
 // EST RFC 7030 hardening master bundle Phase 5.2.

internal/pkcs7/pkcs7.go

@@ -1,3 +1,6 @@
+// Copyright 2026 certctl LLC. All rights reserved.
+// SPDX-License-Identifier: BUSL-1.1
+
 // Package pkcs7 provides ASN.1 helpers for building PKCS#7 structures.
 // Used by EST (RFC 7030) and SCEP (RFC 8894) protocol handlers.
 // No external dependencies — hand-rolled ASN.1 encoding only.

internal/pkcs7/signedinfo.go

@@ -1,3 +1,6 @@
+// Copyright 2026 certctl LLC. All rights reserved.
+// SPDX-License-Identifier: BUSL-1.1
+
 // SignerInfo parser + signature verifier for SCEP PKIMessage.
 //
 // RFC 5652 §5 (SignedData) + RFC 8894 §3.2.1 (SCEP authenticatedAttributes).