Cleaning main.rs

[Escoto]

Description

• main.rs: ~65 lines — just module declarations, imports, and the orchestration body
• startup.rs: ~190 lines — all 7 helper functions + WorkspaceSetup struct + SharedRateLimiter type alias, all pub(crate)

Checklist

• Tests added or updated
• cargo clippy -- -D warnings passes
• cargo fmt --check passes
• Documentation updated (if applicable)