feat: add mcap recorder control and cnats providers

Register an MCAP recorder service on the streamer control subjects, reuse the shared recording request and status model, and expose the zed recording preview/conversion helper.

This also replaces the temporary cnats boolean with the explicit CVMMAP_CNATS_PROVIDER modes and documents the supported system and workspace build paths.

src/config/runtime_config.cpp

@@ -155,7 +155,7 @@ std::expected<EncoderDeviceType, std::string> parse_encoder_device(std::string_v
 	return std::unexpected("invalid encoder device: '" + std::string(raw) + "' (expected: auto|nvidia|software)");
 }
 
-std::expected<McapCompression, std::string> parse_mcap_compression(std::string_view raw) {
+std::expected<McapCompression, std::string> parse_mcap_compression_impl(std::string_view raw) {
 	if (raw == "none") {
 		return McapCompression::None;
 	}
@@ -481,6 +481,10 @@ void finalize_rtp_endpoint(RuntimeConfig &config) {
 
 }
 
+std::expected<McapCompression, std::string> parse_mcap_compression(std::string_view raw) {
+	return parse_mcap_compression_impl(raw);
+}
+
 RuntimeConfig RuntimeConfig::defaults() {
 	return RuntimeConfig{};
 }