fix: resolve security issues, deadlocks, and clean up dead code

[moisesvalero]

This Pull Request addresses the security, quality, and bug findings from the comprehensive repository audit.

Changes Implemented:

1. Security Fixes:

   • Switched to Base64 -EncodedCommand\ in \PowerShellEngine.cs\ and \CommandRepair.cs\ to prevent command injection risks.
   • Moved the Gemini API key from the request URL query parameters to request headers (\x-goog-api-key) in \GeminiProvider.cs.
   • Whitelisted allowed targets in \MainViewModel.AbrirAccion\ to block arbitrary file/process execution.
   • Added regex parameter validation for \IniciarServicio\ in \MainViewModel.cs.
   • Added \settings.json\ (where the WPF app stores API keys in plaintext) to .gitignore.

2. Bug & Robustness Fixes:

   • Fixed potential deadlocks in \CommandRepair.RunRedirectedAsync\ and \PowerShellEngine.RunPowerShellAsync\ by reading StandardOutput and StandardError streams concurrently.
   • Wrapped JSON deserialization in \PowerShellEngine.CollectAllAsync\ in a try-catch block for \JsonException.
   • Added try-catch exception handling in \MainViewModel.ScanAsync\ to prevent the WPF app from crashing on diagnostic collection errors.
   • Simplified redundant exception checking for \OperationCanceledException\ / \TaskCanceledException\ in \LlmService.cs.

3. Performance & Cleanups:

   • Removed dead code files \IColector.cs\ and \DiagnosticContext.cs.
   • Removed unused commands (\DownloadModelCommand, \CancelRepairCommand, \ToggleExpandirCommand) and properties (\ScoreColor) from \MainViewModel.cs.
   • Refactored \ChatMessages, \Modulos, and \Problemas\ lists in \MainViewModel.cs\ to use \ObservableCollection\ instead of triggering full list re-renders.
   • Cached compiled \Regex\ instances in \PrivacyFilter.cs.
   • Made \PrivacyFilter's serial anonymization case-insensitive to catch mixed-case serial numbers.
   • Fixed spelling typo in \RulesProvider.cs\ (\Paperas\ -> \Papelera).
   • Mapped \SO.Instalado\ and \SO.UltimoArranque\ properties in \PowerShellEngine.MapToDiagnostico.
   • Replaced duplicate byte-to-GB magic numbers in \HardwareInfo.cs\ with a named constant \BytesPerGB.