Improve macOS layout shortcuts for v0.3.4

[andy5090]

What changed

• added a one-row top margin when the big-font zone is disabled without starving compact terminals
• added Shift+F5 as a platform-neutral line-spacing shortcut while keeping Option+L / Alt+L as alternates
• clarified macOS Option, Control, Command, Windows, and function-key notation in help and README
• kept primary reading and sound shortcuts visible in adaptive footer guidance
• bumped Termleaf to v0.3.4

Why

macOS terminals may not deliver Option+L consistently, and the document started flush against the top edge when big text was disabled. Modifier labels also needed to match the physical keys users see on each operating system.

Validation

• cargo fmt --all -- --check
• cargo test --all-features (82 tests)
• cargo clippy --all-targets --all-features -- -D warnings
• cargo build --release
• git diff --check

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Keep alternate shortcuts from displacing primary help

On terminals 15–16 rows high, draw_help can display only 8–9 content lines and always truncates from the end. Inserting this optional alternate-shortcut line before the Sound and Other lines therefore makes the F10 guidance disappear at 15 rows and the quit/help guidance disappear at 16 rows; previously those lines were visible at those respective heights. Move or combine the alternate notation so primary controls remain reachable in short-terminal help.

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