Merge Time Entries

Request model for folding 1..N time entries into another one.

Backs the desktop gesture of dropping one or more entries onto another entry's row. Every source's time blocks move to the target and each source is discarded; the target keeps its own narrative, matter/segment, activity code and billable flag — see docs/decisions/0008-a-merge-keeps-the-target-entry.md.

Nothing about the surviving entry's content is client-supplied. In particular the resulting legal time is the server's to decide (resolve_merged_legal_time), because the rule depends on whether each figure was typed by a person — state the client mirrors but does not own.

Partial-success envelope for a merge.

Every row is in cursor-sync wire shape and carries its post-mutation version, so the desktop client force-applies the whole response to its local SQLite mirror rather than waiting a round: the target row gains the minutes, the discarded rows arrive as tombstones and evict, and the moved blocks re-parent.

A source in failed ships no row data — the server never touched it, so the client's local row is already correct. When failed accounts for every source, nothing was written at all and time_entry is the untouched target.