feat: add NATS + Dapr infrastructure for event-driven architecture

- infra/compose/nats.yml: NATS server with JetStream, persistence volume, healthcheck
- infra/compose/dapr.yml: Dapr placement service for sidecar coordination
- infra/dapr/: Dapr global config, pubsub component (NATS), statestore (Redis)
- infra/compose/scraper.yml: add Dapr sidecar container + depends_on nats/dapr
- docs/add-dapr-service.md: guide for integrating Dapr into new services
- docs/add-new-app.md: add Dapr sidecar step
- ARCHITECTURE.md: add NATS/Dapr to infra table + service mesh diagram
- infra/README.md: update layout and deployment order
- deploy-docker.yml: add nats.yml + dapr.yml to ALL_COMPOSE_FILES

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

CHANGELOG.md

@@ -17,6 +17,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Optimized `scraper.Dockerfile`: removed Node.js and Chromium from runtime image.
 - Simplified CI/CD workflows: removed orphan container reference, commented code blocks.
 - Cleaned up scripts: removed stale MySQL config, fixed package references, simplified update-deps.
+- Added NATS + JetStream message broker infrastructure (`infra/compose/nats.yml`).
+- Added Dapr runtime infrastructure: placement service, sidecar pattern, pub/sub + state store components.
+- Integrated Dapr sidecar into scraper service (`infra/compose/scraper.yml`).
+- Updated deployment order: shared → NATS → Dapr → Traefik → apps.
+- Added `docs/add-dapr-service.md` guide for adding Dapr to new services.
 
 ### Removed