feat: home-directory install path, offline mode, caching, and fixes

[DaFa66]

*NIX script alignment

• Install path moved from c:\webstack to %USERPROFILE%\getphp (e.g. C:\Users<you>\getphp) — aligns with the Unix/Mac getphp.sh convention of ~/getphp
• Log files centralised to %USERPROFILE%\getphp\logs\ — Apache, PHP, and MariaDB logs now share a single directory

Features

• Offline mode — .\getphp.ps1 -Offline skips URL resolution and downloading, uses pre-cached zips from %TEMP%\webstack_downloads- Sodium PHP extension enabled by default — required by phpMyAdmin v6.0.0 when installed via offline mode
• Download caching — component zips, SQLite3 DLL, and VC++ Redistributable installer persist in %TEMP%\webstack_downloads\ and are reused when the version hasn't changed

Fixes

• Offline phpMyAdmin — zip was identified but never extracted; now handled alongside Apache, PHP, and MariaDB
• Offline Apache flattening — Invoke-ExtractZip now handles multi-file zips
• Log cleanup on delete — logs/ directory now removed when stack is deleted
• MariaDB logging — my.ini written with log-error path before initialization

Refactoring

• Service registration deduplicated — identical Apache + MariaDB service install code appeared in 3 places; now routes through Install-AsServices (20+ lines removed, single source of truth)