Fix force termination access denied crash

[ZheLZZ]

What changed

• Recognize access-denied errors wrapped by AggregateException when Windows cannot terminate every process in a process tree.
• Return the existing AccessDenied result so TrayTidy can continue into its administrator-elevation flow instead of terminating the WPF application.
• Contain unexpected termination-service exceptions at the current cleanup operation, record a safe failure message, and keep the main interface running.
• Add regression coverage for wrapped access-denied errors, other aggregate failures, and command-level exception containment.
• Update the application version to 0.2.1-beta.

Why

Process.Kill(entireProcessTree: true) can throw an AggregateException whose inner exception is Win32 error 5 (Access is denied). The previous implementation caught only a direct Win32Exception, so the wrapped error bypassed the administrator-elevation branch, reached the WPF dispatcher, displayed a fatal interface-error dialog, and exited TrayTidy.

User impact

Protected or privileged background processes now follow the expected Windows administrator-confirmation path. If Windows or a termination provider returns another unexpected error, TrayTidy reports the individual operation as unsuccessful without closing the whole application.

This change does not alter recommendation scores, default selections, protection rules, process-identity validation, foreground-window checks, modal-dialog checks, or the requirement for explicit user confirmation before force termination.

Validation

• Full Release test suite: 142 passed (Core 47, Persistence 14, Windows integration 30, AI 51).
• Self-contained win-x64 publish completed successfully with product version 0.2.1-beta.
• Release ZIP extracted and compared file-by-file with the publish directory using SHA-256.
• Package contains no PDB, database, log, environment, or private-key files.