refactor(commands): make the complete debug group portable (FEAT-029)

[aboimpinto]

Make the entire debug slash-command group portable

The initial diagnostics migration left receipts and mutation/change commands coupled to App/TUI. The entire fourteen-command group needs a real portable source closure before physical extraction.

Acceptance criteria:

1. All fourteen commands and aliases use portable handlers with exact facets and safe missing-authority behavior.
2. Receipt and result/action shapes belong to the shared contract; compile the actual complete group normally without TUI or stand-in transport types.
3. Preserve output, parsing, localization, receipts and mutation/snapshot safety using meaningful fake/real host tests.
4. Discover every actual debug source while preserving immutable migration topology; retire debug truthfully.
5. Pass CodeWhale's CI-aligned full test/doctest/build/lint checks and scoped guards.

Implementation context: #6145 / #5316. This bounded issue must not close the broader adoption effort.

Delivery: draft PR #6707. Local verification is complete; hosted workflows await administrator approval.

Paulo Aboim Pinto