[rust-launcher] Refactor main.rs into smaller logical modules

[barakeinav1]

Context

Follow-up from PR #2326 (port node launcher to Rust). Tracked in #2598.

Problem

crates/tee-launcher/src/main.rs is ~1,279 lines mixing orchestration, registry interaction, image validation, compose rendering, config injection, and tests. This makes it hard to navigate and maintain.

Suggested Module Split

Module	Contents	~Lines
registry.rs	RegistryInfo trait, DockerRegistry, get_manifest_digest()	450
validation.rs	validate_image_hash(), docker pull/inspect logic	150
compose.rs	render_compose_file(), launch_mpc_container()	150
selection.rs	select_image_hash()	100
config.rs	intercept_node_config(), insert_reserved()	100
main.rs	Entry points main() and run() only	100-150

Tests should move to their respective modules.

Action

• Extract modules along the boundaries above
• Move tests to their respective modules
• Keep main.rs as orchestration-only (~100-150 lines)
• Ensure all pub(crate) visibility is correct after split