feat: align LegacyHUB with TeamHUB platform contract (D2/D4, assets, security)

Close 12 audit-driven platform-compliance gaps on a single branch.

- D4 dispatch: app/integrations/dispatch_client.py participant `legacyhub`,
  emits LegacyhubDocumentIndexed + AssetDerivativeReady after the indexing
  commit (idempotent uuid5), http_inbox route (reindex/tombstone) with
  audit-based dedupe; docs/dispatch-contract.md. Celery+Redis stays intra-module.
- D2 SSO: app/integrations/identity.py validates X-TeamHub-* + role/scope
  mapper; security.py adds trusted-header enforcement (AUTH_REQUIRE_IDENTITY)
  and a scope check on /search; docker-compose.teamhub.yml (external teamhub_net
  + internal db net, api not host-published); RUNBOOK network/firewall section.
- Asset standard: SearchHit/Citation carry asset_id/owner_module; buckets
  renamed teamhub-legacyhub-* (+quarantine/tmp/exports); purge-by-asset_id with
  legal-hold guard (app/indexing/projection.py); OCR-markdown derivative event.
- audit_log model + Alembic 0003 + record_audit on writes (same transaction).
- Secret masking: app/common/json_logger.py recursive mask wired into structlog
  (+ensure_ascii=False); event payloads redacted before persistence.
- Service X-API-Key mandatory on ingest endpoints (defence-in-depth).
- Port: host API 8000->8050 (collision with SalesHUB/MailHUB resolved),
  container still listens on 8000.
- Config: no plaintext secret defaults; fail-loud in non-dev (no value leak).
- Docs drift: README PG 5440, layered-auth note, 5173 removed from CORS;
  ingest/folder gated by ENABLE_FOLDER_INGEST (410 by default).
- ADRs: layers mapping, shared-core extraction, UI locale (RU-first).

Tests: 78 passing (ruff, compileall, pytest, tsc, vite build, compose config).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/main.py

@@ -9,8 +9,13 @@ from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
 from app import __version__
-from app.api import routes_health, routes_ingestion, routes_search
-from app.api.security import install_api_key_auth
+from app.api import (
+    routes_dispatch_inbox,
+    routes_health,
+    routes_ingestion,
+    routes_search,
+)
+from app.api.security import install_api_key_auth, install_trusted_headers_auth
 from app.config import settings
 from app.logging_config import configure_logging, get_logger
 
@@ -48,10 +53,12 @@ app.add_middleware(
     max_age=3600,
 )
 install_api_key_auth(app)
+install_trusted_headers_auth(app)
 
 app.include_router(routes_health.router, prefix=settings.app_api_prefix)
 app.include_router(routes_ingestion.router, prefix=settings.app_api_prefix)
 app.include_router(routes_search.router, prefix=settings.app_api_prefix)
+app.include_router(routes_dispatch_inbox.router, prefix=settings.app_api_prefix)
 
 
 @app.get("/")