refactor(cli): split main entrypoint helpers

[peters]

Purpose

• split crates/surge-cli/src/main.rs into focused clap and bootstrap helper modules
• keep main and the runtime dispatch flow at the existing entrypoint path
• remove the surge-cli main baseline entry from the maintainability tracker

Behavior Impact

• no intended behavior change
• CLI command shapes, flags, defaults, parse tests, installer auto-detection, and runtime dispatch stay intact
• maintainability tracking now focuses on the two install command files, delta, and installer UI

Test Evidence

• cargo check -p surge-cli
• cargo test -p surge-cli
• cargo clippy -p surge-cli --all-targets --all-features -- -D warnings -W clippy::pedantic
• ./scripts/check-maintainability.sh
• ./scripts/sync-surge-core-vendor.sh --check
• ./scripts/check-version-sync.sh
• cargo fmt --all -- --check
• RUSTFLAGS="-D warnings" cargo test --workspace
• cargo clippy --all-targets --all-features -- -D warnings
• cargo clippy --workspace --lib --bins --examples -- -D warnings -D clippy::unwrap_used -D clippy::expect_used
• cargo clippy --workspace --all-targets --all-features -- -D warnings -W clippy::pedantic
• dotnet format dotnet/Surge.slnx --verify-no-changes
• dotnet test dotnet/Surge.slnx --configuration Release

Migration Notes

• none