Adds the live-mutation pipeline for active/degraded topologies:
* TopologyMutation table with composite index (state, topology_id)
so the watch-loop guard query stays O(log n).
* claim_next_mutation is a single atomic UPDATE ... WHERE
state='pending' so racing reconcilers deterministically pick one
winner; losers see rowcount=0 and skip.
* reconcile_topologies drains pending rows per live topology, applies
via decnet.mutator.ops.dispatch, and on failure marks the mutation
failed + transitions topology to degraded.
* run_watch_loop gains a gated branch: flat-fleet mutate_all runs
every tick unchanged; the reconciler only enters when the cheap
has_pending_topology_mutation guard returns True.
* apply_* ops re-check hard invariants (names, IP collisions, subnet
overlap, known services, service_config shape) after every mutation
so the repo never lands in an invalid state.
* CLI: 'decnet topology mutate' / 'mutations' subcommands.
anti
a76b9ecdf9