v0.23.0 — gRPC protocol bridge (dds::bridge::grpc)

Added

• dds::bridge::grpc (include/dds/bridge/grpc/{grpc.hpp,transport.hpp,config.hpp}, src/bridge/grpc/{grpc.cpp,transport.cpp,config.cpp}) — a gRPC gateway bridging a dds::IParticipant to RPC clients over JSON-encoded messages, the first item of ROADMAP.md's "Tier 4 — bridges" and a C++ port of go-DDS's bridge/grpc package. Landed as the first member of a new cppdds_bridges CMake target (CPPDDS_BUILD_BRIDGES, default ON) — the first concrete piece of the previously-proposed ddsbridges target group; cppdds_lib itself is untouched. SubscribeRequest/PublishRequest/Sample/PublishAck and their JSON codec are byte-exact with go-DDS's encoding/json.Marshal output, verified against reference vectors captured from a real go-DDS process. Bridge implements the three RPCs (subscribe/publish/stream_publish) as plain C++ methods against SampleSender/PublishReceiver abstractions, independent of any networking, plus lazy subscriber/publisher caching, Options (auth_token/qos/filter/transform), and check_auth(). transport.hpp's Server/Client speak a real, working TCP wire protocol (a text header block plus real gRPC length-prefixed-message framing) rather than a full HTTP/2 gRPC transport — this repo has no HTTP/2 or protobuf dependency anywhere — documented in full in grpc.hpp's file-level scope note. config.hpp/config.cpp hand-roll a minimal YAML-subset parser for the bridge's listen/auth_token/topics schema.
• Verified with 41 new tests (tests/test_bridge_grpc.cpp) — 581/581 tests total. REQ-BRIDGE-GRPC-001 through REQ-BRIDGE-GRPC-011 added, traced and tested. ROADMAP.md's grpc bullet checked off (wan/rest remain open).