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/api/routes_dispatch_inbox.py

@@ -0,0 +1,30 @@
+"""Dispatch HTTP inbox endpoint (D4 / DISPATCH_DELIVERY_MODE=http_inbox).
+
+Receives inbound command/event envelopes from dispatch-api and returns a
+business confirmation. Authenticated as a service participant via X-API-Key.
+"""
+
+from __future__ import annotations
+
+from fastapi import APIRouter, Depends
+
+from app.api.schemas import DispatchConfirm, DispatchEnvelope
+from app.api.security import require_service_api_key
+from app.integrations.dispatch_client import handle_inbox_message
+
+router = APIRouter(tags=["dispatch"])
+
+
+@router.post(
+    "/dispatch/inbox",
+    response_model=DispatchConfirm,
+    dependencies=[Depends(require_service_api_key)],
+)
+def dispatch_inbox(envelope: DispatchEnvelope) -> DispatchConfirm:
+    result = handle_inbox_message(envelope.model_dump())
+    return DispatchConfirm(
+        status=result.get("status", "confirmed"),
+        event_id=envelope.event_id,
+        handled=result.get("handled"),
+        duplicate=result.get("duplicate"),
+    )