fix: harden auth and investment synchronization

Resolve A01-A10 and C01-C07 from the backend audit.
Preserve auth failures, forced candle reconciliation and forecast freshness.
Validate MOEX responses and nested HTTP errors; remove unused legacy paths.

Verified: 209 unit tests, 262 SQLite e2e tests on Linux, OpenAPI and durability.
Record the remaining macOS native SQLite abort in the audit.

src/modules/investments/instruments/application/instrument-market.ts

@@ -1,5 +1,4 @@
 import { MILLISECONDS_PER_SECOND } from '../../../../common/time';
-import { ServiceUnavailableException } from '@nestjs/common';
 import type {
   TbankCandle,
   TbankTimestamp,
@@ -36,16 +35,3 @@ export function previousClose(
     null
   );
 }
-export async function optional<T>(
-  operation: () => Promise<T>,
-  name: string,
-  unavailable: string[],
-): Promise<T | null> {
-  try {
-    return await operation();
-  } catch (error) {
-    if (!(error instanceof ServiceUnavailableException)) throw error;
-    unavailable.push(name);
-    return null;
-  }
-}