Add a token-scoped +undo shortcut that reverses recent sheet edits made
through the sheet-ai write tools, by invoking the undo_last write tool.

- +undo [--steps N | --op NAME]: undo the last N steps, or a named op
- thread a session-stable transaction id (LARK_CLI_SHEET_TRANSACTION_ID)
  into the tool request's extra.transaction_id, so a group of edits and a
  later +undo share one server-side undo stack; omitted when unset to
  preserve per-request behavior
- flag-defs + generated defs for the new shortcut

buildToolBody attached extra.transaction_id to every tool invocation,
including read tools (get_cell_ranges, get_range_as_csv, search_data,
get_workbook_structure, ...). A read scoped to a transaction id resolves
against that transaction's snapshot instead of the live document, so
reads returned blank cells whenever LARK_CLI_SHEET_TRANSACTION_ID was
set. Gate the extra block to ToolKindWrite — the undo stack only ever
concerns writes — by threading kind into buildToolBody at every call
site. Adds a regression test that read tools omit the transaction id.

Without LARK_CLI_SHEET_TRANSACTION_ID set, every CLI write received a fresh
server-minted transaction id, so a group of edits and a later +undo never
shared an undo stack and +undo could not reach the prior writes.

Resolve the write tool's extra.transaction_id in three tiers:
  1. $LARK_CLI_SHEET_TRANSACTION_ID — explicit caller override.
  2. else a value derived from the OS session (getsid on unix, falling back
     to the parent pid; salted with uid and boot/host) so edits in one shell
     session group by default, with no env var to set. Each invocation is a
     fresh process and recomputes the same id rather than persisting one.
  3. else "" — the server mints a per-request id as before.

The derivation never needs the spreadsheet token (undo read-back is already
keyed by token + transaction id), so buildToolBody keeps its signature and
reads still never carry the id.