[codex] Complete root connector exports

[createMonster]

Summary

• Re-export connector types for every active exchange from the crate root.
• Add a public API compile test that verifies the root connector surface stays complete.
• Update docs/ARCHITECTURE.md to describe root exports as connector-type only, with exchange modules remaining the home for builders and exchange-specific details.

Root Cause

src/lib.rs exposed only a subset of active connector types. That made the crate root look like an incomplete public API surface while the active exchange list lives under lotusx::exchanges.

Validation

• cargo test --test public_api --all-features fails before the export change and passes after it
• cargo fmt --all -- --check
• cargo clippy --all-targets --all-features -- -D warnings
• cargo test --all-features
• cargo doc --no-deps --document-private-items --all-features
• cargo audit exits 0 with existing allowed warnings for dotenv, rustls-pemfile, keccak, and rand
• cargo run