feat: replace REST API with gRPC service

Complete migration from FastAPI/HTTP to gRPC:

Proto definition (proto/daena/v1/daena.proto):
- Daena service with 9 RPCs: GetStatus, GetHealth, GetConfig,
  ListPlugins, GetQueueState, ListPendingRecords, ListDeadRecords,
  ListSinks, ReloadConfig
- Messages for all request/response types with proper field types

gRPC server (src/daena/api/grpc_server.py):
- Async gRPC aio server with DaenaServicer implementation
- DaenaGRPCServer with start/stop/serve_forever lifecycle
- All endpoints delegate to DaenaRuntime

gRPC client (src/daena/cli/main.py):
- CLI now uses grpc.insecure_channel + DaenaStub
- Same commands: status, health, queue, sinks, plugins, config, version

Config changes:
- Remove FastAPI/uvicorn/http config, replace with grpc config
- GRPCConfig with host/port/max_workers

Dependency changes:
- Remove fastapi, uvicorn, starlette, anyio
- Add grpcio, grpcio-tools, protobuf
- Keep httpx for HTTP sink forwarding (separate from management API)

Tests:
- 8 new gRPC integration tests (test_grpc.py)
- All 31 tests passing, ruff clean

tests/test_grpc.py

@@ -0,0 +1,105 @@
+from __future__ import annotations
+
+import asyncio
+
+import grpc  # noqa: I001
+import pytest
+
+from daena.api.grpc_server import DaenaGRPCServer
+from daena.api.pb2 import daena_pb2 as pb2
+from daena.api.pb2 import daena_pb2_grpc as pb2_grpc
+from daena.config import DaenaConfig, SinkConfig, SourceConfig
+from daena.core.runtime import DaenaRuntime
+
+
+@pytest.fixture
+async def grpc_env():
+    config = DaenaConfig()
+    config.sources = [
+        SourceConfig(name="dummy", type="dummy", options={"interval": 0.2, "message": "test"})
+    ]
+    config.sinks = [SinkConfig(name="log", type="dummy")]
+    config.persistence.lmdb.path = "/tmp/daena_grpc_test"
+    config.api.grpc.port = 18642
+
+    runtime = DaenaRuntime(config)
+    await runtime.start()
+
+    server = DaenaGRPCServer(runtime, host="127.0.0.1", port=18642)
+    await server.start()
+
+    channel = grpc.aio.insecure_channel("127.0.0.1:18642")
+    stub = pb2_grpc.DaenaStub(channel)
+
+    yield runtime, stub, server
+
+    await channel.close()
+    await server.stop()
+    await runtime.stop()
+
+
+@pytest.mark.asyncio
+async def test_get_status(grpc_env) -> None:
+    _, stub, _ = grpc_env
+    resp = await stub.GetStatus(pb2.Empty(), timeout=5)
+    assert resp.service == "daena"
+    assert resp.version == "0.1.0"
+    assert resp.running is True
+
+
+@pytest.mark.asyncio
+async def test_get_health(grpc_env) -> None:
+    _, stub, _ = grpc_env
+    resp = await stub.GetHealth(pb2.Empty(), timeout=5)
+    assert resp.healthy is True
+    assert resp.running is True
+
+
+@pytest.mark.asyncio
+async def test_get_config(grpc_env) -> None:
+    _, stub, _ = grpc_env
+    resp = await stub.GetConfig(pb2.Empty(), timeout=5)
+    assert resp.config_json != ""
+
+
+@pytest.mark.asyncio
+async def test_list_plugins(grpc_env) -> None:
+    _, stub, _ = grpc_env
+    resp = await stub.ListPlugins(pb2.Empty(), timeout=5)
+    assert len(resp.sources.items) > 0
+    assert len(resp.sinks.items) > 0
+
+
+@pytest.mark.asyncio
+async def test_get_queue_state(grpc_env) -> None:
+    _, stub, _ = grpc_env
+    await asyncio.sleep(1)
+    resp = await stub.GetQueueState(pb2.Empty(), timeout=5)
+    assert resp.total > 0
+    assert resp.pending > 0
+
+
+@pytest.mark.asyncio
+async def test_list_pending_records(grpc_env) -> None:
+    runtime, stub, _ = grpc_env
+    await asyncio.sleep(1)
+    req = pb2.Pagination(limit=10, offset=0)
+    resp = await stub.ListPendingRecords(req, timeout=5)
+    assert resp.count > 0
+    assert len(resp.records) > 0
+    assert resp.records[0].record_id != ""
+
+
+@pytest.mark.asyncio
+async def test_list_sinks(grpc_env) -> None:
+    _, stub, _ = grpc_env
+    resp = await stub.ListSinks(pb2.Empty(), timeout=5)
+    assert len(resp.sinks) >= 1
+    assert resp.sinks[0].name == "log"
+
+
+@pytest.mark.asyncio
+async def test_reload_config(grpc_env) -> None:
+    _, stub, _ = grpc_env
+    resp = await stub.ReloadConfig(pb2.Empty(), timeout=10)
+    assert resp.success is True