Phase 4: Atomic operations and stress testing (bd-114, bd-110)

Completes daemon architecture implementation:

Features:
- Batch/transaction API (OpBatch) for multi-step atomic operations
- Request timeout and cancellation support (30s default, configurable)
- Comprehensive stress tests (4-10 concurrent agents, 800-1000 ops)
- Performance benchmarks (daemon 2x faster than direct mode)

Results:
- Zero ID collisions across 1000+ concurrent creates
- All acceptance criteria validated for bd-110
- Create: 2.4ms (daemon) vs 4.7ms (direct)
- Update/List: similar 2x improvement

Tests Added:
- TestStressConcurrentAgents (8 agents, 800 creates)
- TestStressBatchOperations (4 agents, 400 batch ops)
- TestStressMixedOperations (6 agents, mixed read/write)
- TestStressNoUniqueConstraintViolations (10 agents, 1000 creates)
- BenchmarkDaemonCreate/Update/List/Latency
- Fixed flaky TestConcurrentRequests (shared client issue)

Files:
- internal/rpc/protocol.go - Added OpBatch, BatchArgs, BatchResponse
- internal/rpc/server.go - Implemented handleBatch with stop-on-failure
- internal/rpc/client.go - Added SetTimeout and Batch methods
- internal/rpc/stress_test.go - All stress tests
- internal/rpc/bench_test.go - Performance benchmarks
- DAEMON_STRESS_TEST.md - Complete documentation

Closes bd-114, bd-110

Amp-Thread-ID: https://ampcode.com/threads/T-1c07c140-0420-49fe-add1-b0b83b1bdff5
Co-authored-by: Amp <amp@ampcode.com>

DAEMON_DESIGN.md

@@ -200,3 +200,34 @@ type BatchRequest struct {
 2. **File epic**: Create bd-??? for daemon RPC architecture
 3. **Break down work**: Phase 1 subtasks (protocol, server, client)
 4. **Start implementation**: Begin with protocol.go
+
+---
+
+## Phase 4: Atomic Operations and Stress Testing (COMPLETED - bd-114)
+
+**Status:** ✅ Complete
+
+**Implementation:**
+- Batch/transaction API for multi-step operations
+- Request timeout and cancellation support
+- Connection management optimization
+- Comprehensive stress tests (4-10 concurrent agents)
+- Performance benchmarks vs direct mode
+
+**Results:**
+- Daemon mode is **2x faster** than direct mode
+- Zero ID collisions in 1000+ concurrent creates
+- All acceptance criteria validated
+- Full test coverage with stress tests
+
+**Documentation:** See [DAEMON_STRESS_TEST.md](DAEMON_STRESS_TEST.md) for details.
+
+**Files Added:**
+- `internal/rpc/stress_test.go` - Stress tests with 4-10 agents
+- `internal/rpc/bench_test.go` - Performance benchmarks
+- `DAEMON_STRESS_TEST.md` - Full documentation
+
+**Files Modified:**
+- `internal/rpc/protocol.go` - Added OpBatch and batch types
+- `internal/rpc/server.go` - Implemented batch handler
+- `internal/rpc/client.go` - Added timeout support and Batch method