fix(ac-0024): injective C identity via SHA-256 length-prefix digest + PostgreSQL migration/round-trip tests

Co-authored-by: genichin <4282227+genichin@users.noreply.github.com>

trex_core/adapters/persistence/sql/026_create_reconcile_notification_state.sql

@@ -1,5 +1,5 @@
 -- req-0007 / ac-0024: durable mismatch notification lifecycle state.
--- PK: identity_key (slot_id TEXT for B-case; "{instance_key}\x00C\x00{symbol}" for C-case).
+-- PK: identity_key (slot_id TEXT for B-case; "C:<sha256_hex>" length-prefix-digest for C-case).
 -- lifecycle_state: 'notified' | 'pending_resolved'.
 -- ON CONFLICT DO UPDATE: replay-safe; re-running migration is a no-op.
 CREATE TABLE IF NOT EXISTS reconcile_notification_state (

trex_core/adapters/portfolio/reconcile_notification_store.py

@@ -4,7 +4,7 @@ Tracks per-identity B/C-case mismatch notification fingerprints so that
 duplicate alarms are suppressed across scheduler ticks and process restarts,
 and pending resolved transitions can be retried.
 
-PK: identity_key (slot_id for B-case; "{instance_key}\\x1fC\\x1f{symbol}" for C-case).
+PK: identity_key (slot_id TEXT for B-case; "C:<sha256_hex>" length-prefix-digest for C-case).
 lifecycle_state: 'notified' | 'pending_resolved'.
 """
 from __future__ import annotations