Add rBroker + wBroker pool, BrokerPayload, NamasteCore trait stub

- src/brokers/: pool manager, r_broker (rec.read), w_broker (rec.write),
  BrokerPayload struct, BrokerError type
- src/core/: NamasteCore trait — fetch/write/update/delete interface, stubs
- IPL step 6: spawns rBroker + wBroker pools after exchange declaration
- tests/broker_pool_test.rs: integration tests for pool spawn (skip if broker down)
- BrokerPayload unit tests + doctest in payload.rs
- Added futures-lite, serde_json to Cargo.toml
- README.md, CLAUDE.md, wiki updated to reflect new structure and status

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/brokers/error.rs

@@ -0,0 +1,33 @@
+//! # brokers/error.rs — Broker Error Types
+//!
+//! Defines the error type for all broker task operations in BEDS.
+//!
+//! ## Calling Agents
+//! - `brokers::r_broker` — returned from spawn and consume operations
+//! - `brokers::mod` — surfaced from pool management
+//!
+//! **Author:** mks
+//! **Version:** 1.0
+//!
+//! ## History
+//! * `2026-04-05` - mks - original coding
+
+/// Errors that can occur in any BEDS broker task.
+///
+/// AMQP protocol errors are wrapped transparently via the `From` impl.
+/// Additional variants cover broker-specific failure modes.
+///
+/// # History
+///
+/// * `2026-04-05` - mks - original coding
+#[derive(Debug, thiserror::Error)]
+pub enum BrokerError {
+    #[error("AMQP protocol error: {0}")]
+    Protocol(#[from] lapin::Error),
+
+    #[error("Broker task '{0}' failed to start: {1}")]
+    StartupFailed(String, String),
+
+    #[error("Message decode error in broker '{0}': {1}")]
+    DecodeFailed(String, String),
+}