feat(delegation): resume an interrupted delegated task with resume_delegation

New codeg-mcp tool that revives a delegated task cut off by a cancel or an
unexpected session/app termination — and ONLY such a task — under its
original task_id: the child's recorded agent session is reloaded via the
row's external_id and a fixed continuation prompt lands in the same
conversation row, whose unchanged delegation_call_id re-arms the lifecycle's
TurnComplete routing, so get_delegation_status / cancel_delegation keep
working on the id the caller already holds.

Strict scope, enforced broker-side: running / completed / failed / foreign
tasks refuse with "not_resumable" and their actual status; a stale
in_progress row resumes only when no live connection is bound to it; the
tool takes no task text (the bounded `reason` is interruption context), so
it cannot become a second delegate_to_agent. A per-task resuming claim
prevents concurrent double-spawns onto one agent session, resuming
atomically clears the stale canceled cache entry with its byte/order
bookkeeping, and failure teardown disconnects a child connection only when
the spawn actually created it (dedup-reused live sessions are left alone).

Wire-through: tool schema + companion arm (delegation feature group, cancel
parity via external_handle), BrokerMessage::ResumeTask transport, listener
arm with identity-less host rename, ConnectionSpawner resume methods on
ConnectionManagerSpawner, plus frontend normalization aliases, a lean
CodegMcpToolCard row and 10-locale labels.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>