feat(export): add AYCD JSON format

[Mathious6]

What changed

• Add a discreet AYCD JSON option to the Export menu and row menu.
• Export the current all, selected, or context-row scope with TXT filename stems as categories.
• Generate pretty JSON with UUID v4 IDs and secure file permissions.
• Share secure file writing across inventory, TXT, and AYCD output.

Layer 4 of native stack #19, above #17.

Closes #14

[Mathious6]

CodeQL flagged four hard-coded password values in AYCD unit fixtures as critical cryptographic values. They were synthetic test strings, not real credentials or production secrets. Replaced them with runtime-generated UUID credentials while preserving the colon-password assertion; no production behavior changed. Local Rust quality gates and all 78 tests pass.