fed-sx-types Phase 6: DefineTrigger verb + trigger_registry

The trigger declaration layer (fed-sx-triggers-loop.md Phase 1): bind an
activity-type to a durable flow so an arriving activity can fan out into
a business flow.

- next/genesis/activity-types/define_trigger.sx — the DefineTrigger verb
  (DefineActivity form, nested-get schema). :object carries
  :activity-type, :flow-name, optional :guard / :actor-scope.
- next/kernel/trigger_registry.erl — pure core + registered gen_server,
  mirroring peer_actors/peer_types. Keyed by activity-type, multiple
  specs per type fire independently. Spec = {TriggerCid, FlowName,
  Guard, ActorScope}. Hydrates on start from a fold over DefineTrigger
  activities (restart-safe, same content-addressing as define_registry).

Manifest activity-types 7->8 (total bundle 38->39); the four bootstrap
count suites + genesis_parse bumped, and bootstrap_load's internal
timeout raised (the larger bundle's double cid:to_string was truncating).

Tests: define_trigger.sh (6), trigger_registry.sh (17). lib/erlang
771/771 + next/flow 34/34 untouched.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

next/tests/bootstrap_start.sh

@@ -121,10 +121,10 @@ check() {
 
 check 10  "bootstrap module loaded"           "bootstrap"
 check 20  "whereis(nx_kernel) is Pid"         "true"
-check 21  "activity_types count = 7"          "7"
+check 21  "activity_types count = 8"          "8"
 check 22  "object_types count = 13"           "13"
 check 23  "projections count = 7"             "7"
-check 24  "total entries = 38"                "38"
+check 24  "total entries = 39"                "39"
 check 25  "fresh log_tip = 0"                 "0"
 check 26  "publish advances tip to 1"         "1"
 check 27  "actor_id = alice"                  "true"