Web: duplicate a planned operation or budget

[corentin-core]

Context

Two planned operations or budgets often differ by one field — an amount, a start date, a category. Creating the second one means retyping the whole form, since the only actions on a target are create, edit, delete and split.

Proposed solution

• Add a "Duplicate" action on the target edit page, opening the creation form pre-filled from the source target.
• Nothing is written until the form is submitted, so the copy can be abandoned.
• The copy carries no link and no iteration decision from the source — those belong to the original.
• Reuse the seeding path already used to create a planned operation from an operation.

Acceptance criteria

• Duplicating a target opens a pre-filled creation form for the same kind, budget or planned.
• Every field is copied, recurrence and end date included.
• Leaving the form without submitting creates nothing.
• The created target holds no link and no iteration decision inherited from the source.
• French translation added and the .mo recompiled.
• User docs updated.