Record sandbox.start events with reuse prop
for both reattach and new-start paths. Extend SandboxSession with
CreatedAt, LastExecAt, and ExecCount fields to power lifecycle metrics.
Set CreatedAt when persisting new sandbox sessions.

Record ssh.connect events with success/failure status in both sandbox
exec and debug flows. Record ssh.command events with exit_code and
interactive flag. Wrap SSH connection failures with ErrSSH sentinel.

Change syncChangesToSandbox and pullChangesFromSandbox signatures to
return patch bytes for telemetry tracking. Record sync_push events with
patch size, duration, and LFS skip count. Record sync_pull events with
patch size, duration, success status, and reject file count. Wrap patch
application failures with ErrPatch sentinel for error classification.

Record sandbox.exec events with overall duration, exit code, sync push/
pull timing, and total patch bytes. Update SandboxSession ExecCount and
LastExecAt after each exec to support lifecycle analytics.

Record run.initiate event before API call with flags for targeted tasks
and initialization parameters.

Record run.complete event when polling detects a completed run, with
result status, wait duration, and whether the caller was in wait mode.

Flush() was firing the HTTP POST in a background goroutine, but the CLI
exits immediately after calling Flush(), killing the goroutine before
the request completes. Make the send synchronous since it only runs at
CLI exit.