feat(api): add MS23 mission control Prisma schema

Add 4 new models for Mission Control:
- AgentConversationMessage: per-agent message storage with SSE streaming
- AgentSessionTree: parent/child subagent relationships (taskSource field for mosaic-queue integration)
- AgentProviderConfig: external provider registration per workspace (encrypted credentials)
- OperatorAuditLog: append-only audit trail for barge-in/kill/pause actions

Closes #693 (partial — schema only)

apps/api/prisma/migrations/20260307004007_ms23_mission_control_schema/migration.sql

@@ -0,0 +1,83 @@
+-- CreateTable
+CREATE TABLE "AgentConversationMessage" (
+    "id" TEXT NOT NULL,
+    "sessionId" TEXT NOT NULL,
+    "provider" TEXT NOT NULL DEFAULT 'internal',
+    "role" TEXT NOT NULL,
+    "content" TEXT NOT NULL,
+    "timestamp" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "metadata" JSONB NOT NULL DEFAULT '{}',
+
+    CONSTRAINT "AgentConversationMessage_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateTable
+CREATE TABLE "AgentSessionTree" (
+    "id" TEXT NOT NULL,
+    "sessionId" TEXT NOT NULL,
+    "parentSessionId" TEXT,
+    "provider" TEXT NOT NULL DEFAULT 'internal',
+    "missionId" TEXT,
+    "taskId" TEXT,
+    "taskSource" TEXT DEFAULT 'internal',
+    "agentType" TEXT,
+    "status" TEXT NOT NULL DEFAULT 'spawning',
+    "spawnedAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "completedAt" TIMESTAMP(3),
+    "metadata" JSONB NOT NULL DEFAULT '{}',
+
+    CONSTRAINT "AgentSessionTree_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateTable
+CREATE TABLE "AgentProviderConfig" (
+    "id" TEXT NOT NULL,
+    "workspaceId" TEXT NOT NULL,
+    "name" TEXT NOT NULL,
+    "provider" TEXT NOT NULL,
+    "gatewayUrl" TEXT NOT NULL,
+    "credentials" JSONB NOT NULL DEFAULT '{}',
+    "isActive" BOOLEAN NOT NULL DEFAULT true,
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "updatedAt" TIMESTAMP(3) NOT NULL,
+
+    CONSTRAINT "AgentProviderConfig_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateTable
+CREATE TABLE "OperatorAuditLog" (
+    "id" TEXT NOT NULL,
+    "userId" TEXT NOT NULL,
+    "sessionId" TEXT NOT NULL,
+    "provider" TEXT NOT NULL,
+    "action" TEXT NOT NULL,
+    "content" TEXT,
+    "metadata" JSONB NOT NULL DEFAULT '{}',
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "OperatorAuditLog_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE INDEX "AgentConversationMessage_sessionId_timestamp_idx" ON "AgentConversationMessage"("sessionId", "timestamp");
+
+-- CreateIndex
+CREATE UNIQUE INDEX "AgentSessionTree_sessionId_key" ON "AgentSessionTree"("sessionId");
+
+-- CreateIndex
+CREATE INDEX "AgentSessionTree_parentSessionId_idx" ON "AgentSessionTree"("parentSessionId");
+
+-- CreateIndex
+CREATE INDEX "AgentSessionTree_missionId_idx" ON "AgentSessionTree"("missionId");
+
+-- CreateIndex
+CREATE UNIQUE INDEX "AgentProviderConfig_workspaceId_name_key" ON "AgentProviderConfig"("workspaceId", "name");
+
+-- CreateIndex
+CREATE INDEX "OperatorAuditLog_sessionId_idx" ON "OperatorAuditLog"("sessionId");
+
+-- CreateIndex
+CREATE INDEX "OperatorAuditLog_userId_idx" ON "OperatorAuditLog"("userId");
+
+-- CreateIndex
+CREATE INDEX "OperatorAuditLog_createdAt_idx" ON "OperatorAuditLog"("createdAt");