apply_update_decky only merged payload.patch into decky_config. Since
services is a separate DB column, there was no way to replace a decky's
services list via a mutation. Add a top-level services key to the op
payload that maps straight onto the services column.
Unblocks the MazeNET editor routing service-add/service-drop actions
through the mutation queue on active topologies.
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.
