Add prefilled query option

[bsg62]

Summary

• Add clap-based CLI parsing with a positional path and optional -q/--query prefill flag.
• Seed the TUI query from the flag and start the search immediately for non-empty prefilled queries.
• Keep help/version available before the TTY guard and add CLI regression tests.

Test Plan

• cargo fmt --manifest-path rust/Cargo.toml -- --check
• cargo clippy --manifest-path rust/Cargo.toml -- -D warnings
• cargo test --manifest-path rust/Cargo.toml
• cargo run --manifest-path rust/Cargo.toml -- --help
• cargo run --manifest-path rust/Cargo.toml -- --version
• normal non-TTY run still exits 2 with the existing terminal error

Manual TUI smoke test still recommended:
cargo run --manifest-path rust/Cargo.toml -- . -q TODO