feat(ttp): E.1.9 API contract — seven router endpoints, admin-gated state mutations, response models

Mounts /api/v1/ttp/* with empty-list / empty-Navigator responses.
GET endpoints viewer-gated; POST/DELETE /rules/{rule_id}/state
admin-gated server-side. POST parses JSON manually so a malformed
body returns the documented 400 (per feedback_schemathesis_400).

Drops xfail-strict markers from E.2.8 tests now that the router is
mounted; 26 tests pass against the contract handlers.

development/TTP_TAGGING.md

@@ -2344,6 +2344,8 @@ unrelated events.
 
 **E.1.9 — API contract** (`decnet/web/router/ttp/`)
 
+**Status:** ✅ done.
+
 - Six FastAPI router files matching the API surface above:
   `api_get_techniques.py`, `api_get_by_identity.py`,
   `api_get_by_attacker.py`, `api_get_by_campaign.py`,