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_read.sh

@@ -102,7 +102,7 @@ check 10  "sections/0 length"               "7"
 check 11  "ends_with_sx create.sx"          "true"
 check 12  "ends_with_sx hello"              "false"
 check 13  "ends_with_sx empty"              "false"
-check 20  "section activity_types count"    "7"
+check 20  "section activity_types count"    "8"
 check 21  "section object_types count"      "13"
 check 22  "section projections count"       "7"
 check 23  "section validators count"        "3"
@@ -111,7 +111,7 @@ check 25  "section sig_suites count"        "2"
 check 26  "section audience count"          "3"
 check 30  "read_genesis returns 7 sections" "7"
 check 31  "first section name"              "activity_types"
-check 32  "first section entry count"       "7"
+check 32  "first section entry count"       "8"
 
 TOTAL=$((PASS+FAIL))
 if [ $FAIL -eq 0 ]; then