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_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"    "5"
+check 20  "section activity_types count"    "7"
 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"       "5"
+check 32  "first section entry count"       "7"
 
 TOTAL=$((PASS+FAIL))
 if [ $FAIL -eq 0 ]; then