feat(track-core): add portable training runtimes

Move scheme and PID training runtime behavior into the pure track_core layer and expose render sinks for injected strip application.

Add ESP compatibility adapters, Python bindings/test scaffolding, and in-memory render support so app_track_bt can consume core render and runtime logic without duplicating it.

Cover circular/linear rendering boundaries, all scheme runtime types, scheme render_to parity, PID sample de-duplication, speed suppression, and live tuning in track-core tests.

include/app_track_decoder.hpp

@@ -0,0 +1,59 @@
+#pragma once
+
+#include <variant>
+#include <vector>
+
+#include "app_track_model.hpp"
+#include "track_core/scheme_decoder.hpp"
+
+namespace app::track {
+
+struct TrackSchemeDecoder {
+	using proto_type                            = track_app_TrackScheme;
+	static inline const pb_msgdesc_t *pb_fields = &track_app_TrackScheme_msg;
+
+	TrackSchemeDecoder() = default;
+
+	[[nodiscard]]
+	static TrackSchemeDecoder from_proto(const proto_type &proto);
+
+	[[nodiscard]]
+	expected<track_core::DecodedScheme, error_t> decode_core() const;
+
+	uint8_t id = 0;
+	std::vector<uint8_t> binary;
+	Color color;
+};
+
+struct TrackSchemeMgr {
+	using proto_type                            = track_app_TrackSchemeMgr;
+	static inline const pb_msgdesc_t *pb_fields = &track_app_TrackSchemeMgr_msg;
+
+	struct Add {
+		using proto_type                            = track_app_TrackSchemeMgrAdd;
+		static inline const pb_msgdesc_t *pb_fields = &track_app_TrackSchemeMgrAdd_msg;
+
+		TrackSchemeDecoder scheme_decoder;
+		error_t err{ESP_OK};
+
+		static Add from_proto(const proto_type &proto);
+	};
+
+	struct Clear {};
+
+	using Unknown = std::monostate;
+
+	enum class MessageType : uint8_t {
+		NONE  = 0,
+		ADD   = 1,
+		CLEAR = 2
+	};
+
+	explicit TrackSchemeMgr() = default;
+
+	static TrackSchemeMgr from_proto(const proto_type &proto);
+
+	std::variant<Unknown, Add, Clear> choice{Unknown{}};
+};
+
+} // namespace app::track