feat(#85): implement CONNECT/DISCONNECT protocol

Implemented connection handshake protocol for federation building on
the Instance Identity Model from issue #84.

**Services:**
- SignatureService: Message signing/verification with RSA-SHA256
- ConnectionService: Federation connection management

**API Endpoints:**
- POST /api/v1/federation/connections/initiate
- POST /api/v1/federation/connections/:id/accept
- POST /api/v1/federation/connections/:id/reject
- POST /api/v1/federation/connections/:id/disconnect
- GET /api/v1/federation/connections
- GET /api/v1/federation/connections/:id
- POST /api/v1/federation/incoming/connect

**Tests:** 70 tests pass (18 Signature + 20 Connection + 13 Controller + 19 existing)
**Coverage:** 100% on new code
**TDD Approach:** Tests written before implementation

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

apps/api/src/federation/federation.module.ts

@@ -6,16 +6,32 @@
 
 import { Module } from "@nestjs/common";
 import { ConfigModule } from "@nestjs/config";
+import { HttpModule } from "@nestjs/axios";
 import { FederationController } from "./federation.controller";
 import { FederationService } from "./federation.service";
 import { CryptoService } from "./crypto.service";
 import { FederationAuditService } from "./audit.service";
+import { SignatureService } from "./signature.service";
+import { ConnectionService } from "./connection.service";
 import { PrismaModule } from "../prisma/prisma.module";
 
 @Module({
-  imports: [ConfigModule, PrismaModule],
+  imports: [
+    ConfigModule,
+    PrismaModule,
+    HttpModule.register({
+      timeout: 10000,
+      maxRedirects: 5,
+    }),
+  ],
   controllers: [FederationController],
-  providers: [FederationService, CryptoService, FederationAuditService],
-  exports: [FederationService, CryptoService],
+  providers: [
+    FederationService,
+    CryptoService,
+    FederationAuditService,
+    SignatureService,
+    ConnectionService,
+  ],
+  exports: [FederationService, CryptoService, SignatureService, ConnectionService],
 })
 export class FederationModule {}