chore: Retrieve engine from DB instead of model.yml

[gau-nernst]

Problem Statement

A lot of code does the following

• Get model entry from DB
• Get path to model.yml. Read model.yml to obtain engine value

e.g.

cortex.cpp/engine/controllers/models.cc

Lines 292 to 297 in b31878d

	yaml_handler.ModelConfigFromFile(
	fmu::ToAbsoluteCortexDataPath(
	fs::path(model_entry.value().path_to_model_yaml))
	.string());
	auto model_config = yaml_handler.GetModelConfig();
	if (model_config.engine == kLlamaEngine) {

cortex.cpp/engine/services/model_service.cc

Lines 495 to 499 in b31878d

	auto yaml_fp = fmu::ToAbsoluteCortexDataPath(
	fs::path(model_entry.value().path_to_model_yaml));
	yaml_handler.ModelConfigFromFile(yaml_fp.string());
	auto mc = yaml_handler.GetModelConfig();
	if (engine_svc_->IsRemoteEngine(mc.engine)) {

This is unnecessary because the DB already has column engine

We must make sure the column engine is registered correctly e.g. Currently downloading single GGUF file does not fill in column engine

cortex.cpp/engine/services/model_service.cc

Lines 75 to 85 in b31878d

	cortex::db::ModelEntry model_entry{
	/* .model = */ ggufDownloadItem.id,
	/* .author_repo_id = */ author_id,
	/* .branch_name = */ branch,
	/* .path_to_model_yaml = */ rel.string(),
	/* .model_alias = */ ggufDownloadItem.id,
	"",
	"",
	/* .status = */ cortex::db::ModelStatus::Downloaded,
	"",
	""};

This is also a prerequisite for #2151

Feature Idea

See above

[github-roushan]

@gau-nernst.
can i take this one