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_populate.sh

@@ -99,8 +99,8 @@ check() {
 check  2  "gen_server loaded"                "gen_server"
 check  3  "registry loaded"                  "registry"
 check  4  "bootstrap loaded"                 "bootstrap"
-check 10  "populate returns total 36"        "36"
-check 20  "activity_types count = 5"         "5"
+check 10  "populate returns total 38"        "38"
+check 20  "activity_types count = 7"         "7"
 check 21  "object_types count = 13"          "13"
 check 22  "projections count = 7"            "7"
 check 23  "validators count = 3"             "3"