[BUG] The macro builder and the conditional branch editor share a drop zone type, with no cross-zone guard

[chhoumann]

Noticed while fixing #1593. Code shape confirmed; I have not driven the drag live, so treat the exploitability as unproven.

MacroBuilder.configureConditionalBranch (MacroBuilder.ts:186-193) opens ConditionalBranchEditorModal over the still-open macro builder. Both modals mount a CommandList, and both register their drop zone with the same svelte-dnd-action type:

CommandList.svelte -> baseDndOptions({ items, dragDisabled, type: "command", ... })

baseDndOptions (dndReorder.ts:60-79) never sets dropFromOthersDisabled, so two zones of the same type are mutually valid drop targets. CommandList also has no TRIGGERS.DROPPED_INTO_ANOTHER strip - compare ChoiceList.svelte:107-109, which added exactly that for the choice list because committing the source list verbatim after a cross-zone drop persists a COPY in both zones. CommandList.svelte does not even import TRIGGERS.

Expected failure modes, if the drag is reachable

• a command dragged from the branch modal into the builder is persisted in BOTH lists
• the copy carries the same id into a list that already contains it, which is the each_key_duplicate shape [BUG] A macro's commands has no read-accessor guard, so a malformed one is unrecoverable through the UI #1593 is about (now survivable, since the editor re-keys it, but it should not happen at all)

Suggested shape

Either set dropFromOthersDisabled: true for command zones (they are never a legitimate cross-zone target - unlike folders, a command has no "move into" gesture), or mirror ChoiceList's DROPPED_INTO_ANOTHER strip. The former looks correct here.

Reproducing it needs a macro with a Conditional, the branch editor open on top, and a pointer drag between the two lists - worth doing before fixing, to confirm the modal stacking actually allows it.