Preserve portable firmware settings in .entlayout

[IgorArkhipov]

Summary

This is the focused follow-up suggested in the closing comment on #93.

It extends manual .entlayout export/import without adding automatic recovery infrastructure.

• Bump .entlayout to v4 and add an optional portable_settings section for advertised standard QMK settings, including Quick Tap, Auto Shift, One Shot, Tap-Hold, Mouse Keys, Magic, Grave Escape, and compatible touchpad settings such as Auto Layer.
• Store a stable semantic ID, QSID, value width, value, and—where applicable—the ordered variants that define a select field's meaning.
• Restore only settings whose target contract matches. Unsupported, malformed, duplicated, or incompatible entries are skipped conservatively.
• Verify every write with immediate exact readback, continue after individual failures, and show imported/unsupported/incompatible/failed counts plus exact write failures in the import report.
• Preserve v1-v3 import compatibility; files without portable_settings continue to load unchanged.

Scope

Existing .entlayout sections remain authoritative for layer names and Combo Term, so they are not duplicated. Keyboard-specific module fields, Layer LED/RGB, and Bluetooth settings are intentionally excluded because their portable contract cannot be established generically across firmware definitions.

This PR does not add serial-backed history, automatic prompts, deferred banners, background capture, or a separate HID recovery lifecycle.

Validation

• cargo test --locked: 320 tests passed
• cargo build --release --locked: passed
• cargo clippy --locked --bin entropy: passed (repository's existing warnings only)
• python3 scripts/check_i18n.py: passed
• rustfmt --edition 2021 --check src/entlayout.rs: passed
• git diff --check: passed