fix: all-users (Common) startup-folder toggles target HKLM, not HKCU

[laurentiu021]

Summary

Fresh ultra-audit finding (services-O-S, P2), verified against current source.

Both the per-user Startup folder and the all-users Common Startup folder were scanned and tagged with the same StartupSource.StartupFolder. So ApplyApprovedState read the enabled/disabled state for all folder items only from HKCU, and SetEnabledAsync wrote the toggle blob for all folder items only to HKCU. But Windows stores the StartupApproved\StartupFolder state for all-users shortcuts under HKLM.

Consequences for a shortcut in %ProgramData%\...\Startup:

• An item disabled via Task Manager (HKLM blob) was shown as "Enabled" (wrong state).
• Disabling it in SysManager wrote the disable blob to HKCU — where Windows never looks for common-folder state — so it returned success while the program still launched at logon.

For a startup manager, a disable that reports success but doesn't disable is a trust/correctness defect.

Fix

• Added StartupSource.CommonStartupFolder, set in ReadStartupFolder based on which special folder produced the entry (SpecialFolder.Startup vs SpecialFolder.CommonStartup).
• ApplyApprovedState now reads HKLM's StartupApproved\StartupFolder for common-folder entries.
• SetEnabledAsync routes common-folder entries to HKLM (needs administrator — a non-elevated attempt surfaces the existing "requires elevation" message, exactly like the HKLM Run path).
• Per-user folder items are completely unchanged.

Regression tests

• BuildStartupFolderEntry_Common_TaggedCommonStartupFolder — isCommon: true → CommonStartupFolder.
• BuildStartupFolderEntry_PerUser_TaggedStartupFolder — isCommon: false → StartupFolder.

Both are red before the fix (the isCommon parameter and the CommonStartupFolder enum value did not exist). The hive routing depends entirely on this source tagging. (No test writes the registry — the toggle's HKLM write path needs elevation and would mutate real machine state, so it's excluded from the CI-safe unit suite.)

Checks

• All 3 projects build 0 warnings / 0 errors
• Leak scan on diff: clean