feat(#1680): ADR-1239 Phase C-1 — hook-bus + stateIO seams [AC4] (#1805)

* feat(#1680): ADR-1239 Phase C-1 — hook-bus + stateIO seams [AC4]

Phase 3 slice 4 (AC4, final #1680 slice). The last two adapter seams behind
the negotiated hookBus/stateIO axes:

- src/hook-bus.cts: createHookBus({bus}, {hostEmit?}) -> host/engine/none.
  engine = in-process pub/sub (handler errors isolated); host = host-owned,
  fail-closed emit until a host emitter is bound; none = silent no-op (degrade
  to rule-text). PORTABLE_EVENT_FLOOR = SessionStart/PreToolUse/PostToolUse/
  Stop/SessionEnd (the claude dialect all hook hosts share).
- src/state-io.cts: createStateIO({io}, {backend?}) -> filesystem (today's
  behavior — straight fs) / sandboxed-storage / session-log-append (fail-closed
  seams until a host backend is bound).

Proactive CI gates: ADR-457 ignores + INVENTORY-MANIFEST entries for both new
.cjs; injection-scan 'act as' substring audit; unused-import check. All clean
locally (11 tests + security 15/15 + inventory + eslint 0 problems).

Phase 3 (#1680) seam layer now complete. Concrete host binding -> Phase 5
(#1682, D15/D18).

* chore(changeset): add Changed fragment for hook-bus + stateIO seams (#1680)

docs/INVENTORY-MANIFEST.json

@@ -335,6 +335,7 @@
       "graphify-command-router.cjs",
       "graphify.cjs",
       "gsd2-import.cjs",
+      "hook-bus.cjs",
       "host-integration.cjs",
       "init-command-router.cjs",
       "init.cjs",
@@ -398,6 +399,7 @@
       "stale-bake-guard.cjs",
       "state-command-router.cjs",
       "state-document.cjs",
+      "state-io.cjs",
       "state-transition.cjs",
       "state.cjs",
       "surface.cjs",