Simplify /tmp permission handling:
- Only check and fix /tmp permissions if they're actually incorrect (not preemptively)
- Remove redundant fix_tmp_permissions() call from prerequisites check
- Keep the fix inline where first_time_install.sh is executed
- When running manually, /tmp usually has correct permissions (1777) so no fix needed
This makes the script less aggressive and avoids unnecessary permission changes
when running manually, while still fixing the issue in automated scenarios.
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