docs: add implementation plan, ADRs, and task tracking system

- Add comprehensive 8-phase implementation plan (docs/plan.md)
- Add 28 Architecture Decision Records (docs/adr/) covering all phases
- Add task tracking system with 283+ task files (docs/stories/)
- Add task generator script for automated task file creation
- Add reference playbooks and requirements documentation

This commit establishes the complete planning foundation for the Go
Platform implementation, documenting all architectural decisions and
providing detailed task breakdown for Phases 0-8.

docs/adr/0023-event-bus-implementation.md

@@ -0,0 +1,59 @@
+# ADR-0023: Event Bus Implementation
+
+## Status
+Accepted
+
+## Context
+The platform needs an event bus for:
+- Module-to-module communication
+- Decoupled event publishing
+- Event sourcing (optional, future)
+- Integration with external systems
+
+Options considered:
+1. **In-process channel-based bus** - Simple, for development/testing
+2. **Kafka** - Production-grade, scalable
+3. **RabbitMQ** - Alternative message broker
+4. **Redis pub/sub** - Simple but less reliable
+
+## Decision
+Support **dual implementation** with **in-process primary, Kafka for production**:
+
+1. **In-process bus (default)**:
+   - Channel-based implementation
+   - Used for development, testing, small deployments
+   - Simple, no external dependencies
+
+2. **Kafka bus (production)**:
+   - Full Kafka integration via `segmentio/kafka-go`
+   - Producer/consumer groups
+   - Configurable via environment (switch implementation)
+
+**Rationale:**
+- In-process bus is simple for development
+- Kafka provides production-grade reliability and scalability
+- Interface abstraction allows swapping
+- Modules don't need to know which implementation
+- Can start simple and scale up
+
+## Consequences
+
+### Positive
+- Simple for development (no Kafka needed)
+- Scalable for production (Kafka)
+- Flexible (can choose implementation)
+- Modules are decoupled from implementation
+
+### Negative
+- Two implementations to maintain
+- Need to ensure interface covers both use cases
+- Kafka adds infrastructure complexity
+
+### Implementation Notes
+- Create `pkg/eventbus/eventbus.go` interface
+- Implement `internal/infra/bus/inprocess_bus.go` (channel-based)
+- Implement `internal/infra/bus/kafka_bus.go` (Kafka)
+- Select implementation via config
+- Support both sync and async event publishing
+- Handle errors gracefully (retry, dead letter queue)
+