chore: vendor library-only cc-switch - #1

Summary

• vendor botiverse/cc-switch-cli commit da39f632730ff72635bcfc4e82253503c4cebf18
• consume the vendored crate with default-features = false
• refresh Cargo.lock, removing the CLI/TUI-only dependency set
• record fork provenance and the corresponding upstream PR

Upstream contribution: SaladDay/cc-switch-cli#421

Validation

• cargo check --locked
• cargo fmt --check
• cargo clippy --all-targets -- -D warnings
• yarn build:debug
• yarn lint
• yarn test (10 passed)
• Taplo and Prettier checks for changed TOML/JSON/Markdown files
• verified the vendored crate's direct dependency graph excludes all CLI/TUI dependencies