Make lg_webos the default TV platform with bscpylgtv fallback

[Staphylococcus]

Summary

• default genuinely fresh profiles to native lg_webos while keeping missing legacy values on bscpylgtv
• require successful native pairing and credential verification before saving fresh configuration
• preserve explicit compatibility selection and cover fresh, legacy, upgrade, and release-bundle paths
• update user/support documentation and release-note guidance

Validation

• cargo fmt --all --check
• cargo clippy -p lg-buddy --all-targets -- -D warnings
• cargo test -p lg-buddy --lib
• full Cucumber suite (124 scenarios, 1,431 steps)
• release-bundle build/install/upgrade/uninstall smoke
• shell syntax checks and git diff --check

Closes #54