Harness: parity golden filenames key on row index, so mid-table inserts rename snapshots

[jernejk]

Parity goldens under tests/SSW.TimePro.Cli.Integration/Mcp/Goldens/Mcp/Parity are named by row index (e.g. CreateTimesheet.9.cli.json). Inserting a row in McpCliParityTable shifts every later index and produces pure renames of byte-identical snapshots (ten in #70). Key the filename on a stable case id (tool wire name plus a short case slug declared on the row) instead, and migrate the existing files once.