feat(#292): implement protocol version checking

Add protocol version validation during connection handshake.
- Define FEDERATION_PROTOCOL_VERSION constant (1.0)
- Validate version on both outgoing and incoming connections
- Require exact version match for compatibility
- Log and audit version mismatches

Fixes #292

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

apps/api/src/federation/constants.ts

@@ -0,0 +1,13 @@
+/**
+ * Federation Protocol Constants
+ *
+ * Constants for federation protocol versioning and configuration.
+ */
+
+/**
+ * Current federation protocol version
+ * Format: MAJOR.MINOR
+ * - MAJOR version: Breaking changes to protocol
+ * - MINOR version: Backward-compatible additions
+ */
+export const FEDERATION_PROTOCOL_VERSION = "1.0";