refactor: use [GeneratedRegex] for SFC/DISM/speedtest literal patterns

[laurentiu021]

Summary

Converts the three remaining literal-pattern Regex.Match call sites to
source-generated [GeneratedRegex] partial methods. The pattern strings are
unchanged, so matching behavior is byte-identical — [GeneratedRegex] just moves
compilation from runtime to build time (no startup Regex construction, no
per-call interpreter overhead).

Changes

• ViewModels/CleanupViewModel.cs
  • SFC progress: Regex.Match(l.Text, @"(\d+)\s*%") → SfcPercentRegex().Match(...)
  • DISM progress: Regex.Match(l.Text, @"([\d.]+)%") → DismPercentRegex().Match(...)
• ViewModels/SpeedTestViewModel.cs
  • Server-id parse: Regex.Match(option, @"ID:\s*(\d+)") → ServerIdRegex().Match(...)
  • Added using System.Text.RegularExpressions; (was fully-qualified before).

Not converted (deliberately)

• LogService line 33 builds its regex from an interpolated pattern
  ($@"(?i)({escaped})...") — a runtime value, so it cannot be source-generated.
  It stays a runtime Regex. The constant fallback pattern there was already
  converted in the earlier [GeneratedRegex] PR.

Verification

• Pattern strings verified identical old→new (diff-checked, no character changed).
• Both VMs are already sealed partial class — the prerequisite for [GeneratedRegex].
• Build: main + Tests + IntegrationTests all 0 warnings / 0 errors.

Behavior identical (Protocol Q). refactor: → no release.