fed-sx-types Phase 1: DefineType + SubtypeOf genesis verbs

Two new DefineActivity-form genesis activity-types for host-type
federation (plans/fed-sx-host-types.md step 1):

- next/genesis/activity-types/define_type.sx — DefineType verb; schema
  accepts an :object with a string :name and optional list :fields.
- next/genesis/activity-types/subtype_of.sx — SubtypeOf verb; schema
  accepts an :object carrying string :child-type-cid + :parent-type-cid.

Schema bodies use nested `get` (not keyword-threading) so they are
directly evaluatable — keywords are not callable getters in the kernel.
Both registered in manifest.sx (activity-types now 7); the four bootstrap
suites' bundle counts bumped (5->7, total 36->38).

Tests: next/tests/define_type.sh (7), subtype_of.sh (6) — parse shape,
schema accept/reject, term_codec envelope round-trip.

Also load follower_graph + delivery in bootstrap_start.sh: its check-26
publish path exercises outbox:compute_delivery_set/3 (follower_graph:new
+ delivery:delivery_set), which an m2 substrate change had left unloaded
in that suite — a pre-existing red unrelated to the count bump.

Conformance 771/771; all touched next/tests green.

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

next/tests/bootstrap_load.sh

@@ -106,7 +106,7 @@ check 10  "strip suffix create.sx -> create"    "true"
 check 11  "strip suffix hello unchanged"        "true"
 check 12  "strip suffix .sx -> empty"           "true"
 check 13  "load_genesis rejects bad shape"      "ok"
-check 20  "loaded activity_types count = 5"     "5"
+check 20  "loaded activity_types count = 7"     "7"
 check 21  "loaded object_types count = 13"      "13"
 check 22  "loaded projections count = 7"        "7"
 check 23  "loaded validators count = 3"         "3"