test(12-01): update all tests for explicit key args, add key input tests

- Replace KEY import in golden.rs with local constant
- Replace KEY import in crypto.rs tests with local TEST_KEY constant
- Add --key to all CLI round-trip tests via cmd_with_key() helper
- Add test_key_file_roundtrip: pack/unpack with --key-file
- Add test_rejects_wrong_key: wrong key causes decryption failure
- Add test_rejects_bad_hex: too-short hex produces clear error
- Add test_rejects_missing_key: pack without key arg fails
- Add test_inspect_without_key: shows header only, not TOC
- Add test_inspect_with_key: shows full entry listing
- All 47 tests pass (25 unit + 7 golden + 15 integration)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/golden.rs

@@ -4,9 +4,16 @@
 //! during 03-RESEARCH. These tests use fixed IVs for deterministic output.
 
 use encrypted_archive::crypto;
-use encrypted_archive::key::KEY;
 use hex_literal::hex;
 
+// Use the legacy hardcoded key for golden test vectors
+const KEY: [u8; 32] = [
+    0x7A, 0x35, 0xC1, 0xD9, 0x4F, 0xE8, 0x2B, 0x6A,
+    0x91, 0x0D, 0xF3, 0x58, 0xBC, 0x74, 0xA6, 0x1E,
+    0x42, 0x8F, 0xD0, 0x63, 0xE5, 0x17, 0x9B, 0x2C,
+    0xFA, 0x84, 0x06, 0xCD, 0x3E, 0x79, 0xB5, 0x50,
+];
+
 /// AES-256-CBC encryption of "Hello" with project KEY and fixed IV.
 ///
 /// Cross-verified: