Fix CLI help text defaults, ranges, and pause-style list

[tamirelazar]

Summary

• ~33 help strings showed constant paths instead of values (stringify! misuse): flags with default_value_t now rely on clap's automatic [default: ...] rendering; the seven Option flags (preset-merged) got literal values verified against config_defaults.rs/validation.rs
• --pause-style help now lists all 12 accepted styles; test-only Args::default() aligned to the real default (minimal) — vignette was never user-visible
• --decay range corrected to the enforced 0.5-0.9999; --ascii-contrast "3.0 = strong" corrected to 2.0 (= MAX_CONTRAST)

Verification

• --help and --explain contain zero :: paths; spot-checked rendered defaults/ranges against validation rules
• fmt, clippy -D warnings (default + all-features)
• cargo test --lib 752 / --all-features 764 / visual regression 46 — all baseline, no test updates needed