feat(ttp): E.1.10 repository contract — TTPMixin with insert_tags + list_techniques_by_{identity,attacker,campaign,session} + list_distinct_techniques

Empty NotImplementedError bodies; the SQL lands at E.3 implementation.
Mixin composed onto SQLModelRepository alongside the existing domain
mixins. Dialect-specific INSERT-OR-IGNORE syntax overrides land in
the per-backend subclasses at E.3 per the dual-DB-backend convention.

development/TTP_TAGGING.md

@@ -2360,6 +2360,8 @@ unrelated events.
 
 **E.1.10 — Repository contract** (`decnet/web/db/sqlmodel_repo/ttp.py`)
 
+**Status:** ✅ done.
+
 - `async def insert_tags(rows: list[TTPTag]) -> int` — bulk upsert
   with `INSERT OR IGNORE` semantics for idempotency.
 - `async def list_techniques_by_identity(uuid: str) -> list[...]`.