[ADD] global_undo: undo/redo backend ops with Ctrl+Z

[QubiQBcn]

Why

You save a wrong change, confirm an order, post an invoice, or delete a record — and there is no Ctrl+Z. Cancel/draft flows, manual fixes, or a restore are the only options. Odoo has no general undo for backend work.

What it does

• Records create / write / unlink and reversible actions (confirm SO/PO, post invoice) as one step per form save.
• Ctrl+Z / Ctrl+Shift+Z and a systray (undo, redo, last 10 steps). Inside inputs, Ctrl+Z stays native.
• History + trash under Settings → Global Undo. Unsafe undos are refused, not forced.

Limits

Skips technical models, ledger rows, mass ops, sudo and non-web-client writes. Does not reverse mail/APIs. Respects accounting integrity.

[polqubiq]

Superseded by #3686 (same branch, opened from @polqubiq).

[polqubiq]

Superseded by #3686.

[QubiQBcn]

Superseded by #3686 (same change, from @polqubiq).