fix: treat [checked] as bool like disabled

[gRoussac]

Summary

• [checked] / [(checked)] use eval_bool like [disabled], so false is not a truthy prop_str in the DOM
• Banana writeback uses (change) + el.checked → Host::set(Value::Bool)
• Dogfood checkbox in two-way fixture + demo-leptos

Closes #85

Test plan

• cargo test -p rangular-parser -p rangular-aot -p rangular-runtime (checked / two_way filters)
• cargo clippy -p rangular-parser -p rangular-aot -p rangular-runtime --all-targets -- -D warnings
• cargo check --manifest-path demo-leptos/Cargo.toml
• Toggle checkbox in demo-leptos two-way panel (unchecked by default; Push from Host sets true)

Made with Cursor

[gRoussac]

Opened from wrong fork (gRoussac). Replacing with Interchouette head.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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