feat(orchestrator): add MS23 per-agent message history and SSE stream endpoints

GET /agents/:id/messages - paginated message history
GET /agents/:id/messages/stream - SSE live stream with replay

Partial #693

apps/orchestrator/Dockerfile

@@ -47,14 +47,11 @@ COPY --from=deps /app/packages/shared/node_modules ./packages/shared/node_module
 COPY --from=deps /app/packages/config/node_modules ./packages/config/node_modules
 COPY --from=deps /app/apps/orchestrator/node_modules ./apps/orchestrator/node_modules
 
-# The repo has apps/orchestrator/prisma/schema.prisma as a symlink for CI use.
-# Kaniko resolves destination symlinks on COPY, which fails because the symlink
-# target (../../api/prisma/schema.prisma) doesn't exist in the container.
-# Fix: remove the dangling symlink first, then copy the real schema file there.
-RUN rm -f apps/orchestrator/prisma/schema.prisma
-COPY apps/api/prisma/schema.prisma ./apps/orchestrator/prisma/schema.prisma
-# pnpm turbo build runs prisma:generate (--schema=./prisma/schema.prisma) from the
-# orchestrator package context — no cross-package project-root issues.
+# apps/orchestrator/prisma/schema.prisma is a symlink → ../../api/prisma/schema.prisma
+# Docker COPY follows symlinks, so the schema file is already present after
+# "COPY apps/orchestrator ./apps/orchestrator" above.
+# pnpm turbo build runs prisma:generate first (which uses --schema=./prisma/schema.prisma)
+# from within the orchestrator package — no cross-package project-root issues.
 
 # Build the orchestrator app using TurboRepo
 RUN pnpm turbo build --filter=@mosaic/orchestrator