New SourceOs variants: Android, IpadOs — routed to android-to-* and
ipad-to-* pattern files respectively. Pattern bodies assume zero terminal
experience; every command explained from first principles with App Store /
iOS analogies.
Dual-boot supplement system: PatternFile::extend() + load_supplement()
in patterns.rs; lib.rs loads dualboot-{windows,macos}.toml on top of the
primary pattern file when migration.dual_boot_with is set. Supplement
covers NTFS dirty flag from Fast Startup, clock skew (RTC local vs UTC),
GRUB overwrite by Windows Update, BitLocker, APFS/HFS+ access, T2 Secure
Boot.
complete_onboarding() now accepts dual_boot_with: Option<String> and
normalises it to "windows"/"macos". Onboarding.vue becomes a 3-step flow:
source OS -> (Linux distro if linux) -> (dual-boot if windows/macos).
Mobile users skip the dual-boot step entirely.
10 new pattern files (8 mobile + 2 supplements), config.rs tests updated.
