fix(server): fail closed on unreadable units and accept symlinked homes

The install guard now fails when the unit exists but cannot be read,
compares homes through realPath so a symlinked T3 home is not refused,
and status checks the home before reading this home's runtime state.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
ca05875a42PR Batch Tester committed on 10/22/2026, 10:06:34 PMparent1baadc6

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