fix(cli): replace dialoguer drop prompt with line-based read for accessibility

[BootstrapperSBL]

Summary

Replaces the dialoguer::Confirm prompt in sqlx database drop with a plain stdin().read_line so that screen readers, large-print users, and anyone relying on terminal echo get predictable behaviour. Closes #4236.

Why

As reported in #4236, the existing prompt uses dialoguer::Confirm with wait_for_newline(true). In that mode dialoguer still puts the terminal into raw input for the Y/N toggle, which causes two separate failure modes:

• Wrapped prompt (large print / narrow terminal): each keypress redraws the whole prompt to flip [Y/n] ↔ [y/N], and screen readers re-parse the full line each time.
• Single-line prompt (wide terminal): keypresses silently flip the default marker with no visual echo and no audible announcement — the user has no feedback that their input registered.

In both cases the pressed key is never displayed and there's no explicit "press Enter" cue.

What changed

• ask_to_continue_drop now writes the prompt with an explicit (y/N) hint and reads a line from stdin.
• No raw mode → keypresses echo naturally, Enter is the only implicit terminator, and screen readers get a normal line-at-a-time interaction.
• The RestoreCursorGuard is gone because the cursor is never hidden.
• --force / -y / non-TTY behaviour is unchanged (only the interactive confirm=true path is touched).

A small pure parse_drop_response helper is introduced and unit-tested so the accept/reject matrix is exercised in CI.

Before / After

Before (wrapped prompt, with a screen reader):

? Drop database at postgres://…? [Y/n]  ← full prompt re-read on every Y press

After:

Drop database at postgres://…? (y/N): y

Keypress echoes, Enter commits, screen readers announce just the single line.

Test plan

• cargo fmt --all -- --check
• cargo clippy --manifest-path sqlx-cli/Cargo.toml -- -D warnings
• cargo test --manifest-path sqlx-cli/Cargo.toml (3 unit + 8 add + 3 migrate tests pass)
• Manual: echo y | cargo run -- database drop -D sqlite://test.db proceeds; echo n and empty input abort.