feat(pool): the pool - stacks, admission, the runner and the scheduler

The allowlists and the instrument checks (mcp_connected, db_answered,
exercised), the stack keys, Stacks and Admission, the Runner that runs one
claude or opencode process per pass, and the Scheduler with its retries,
rate-window pauses, the prompt-prefix warm-up, the seats and the board.
One thread per pass; each worker runs on its own copy of the job.

Every pass runs under the supervisor, so a timeout or an abort takes its
whole tree down; a timed-out pass reports exit -9, a SIGKILLed child's
code. The helpers the lenses run are this binary's `sql` and `totp`.
:Process gains an Append stream for the OpenCode meta line.

The tests cover the pool and its share of the commits-mode, seat-pool and
several-drivers checks, a fake claude under the supervisor included.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

interfaces/Crafter.Review-Process.cppm

@@ -32,6 +32,9 @@ export namespace Crafter::Review::Process {
             // Opened for reading (stdin) or created and truncated (stdout,
             // stderr).
             File,
+            // stdout or stderr after what the file already holds: a line the
+            // driver wrote before the child starts stays first.
+            Append,
             // A pipe whose other end Start() returns.
             Pipe,
         };