Author SysRS-310 ratifying the macOS minimum runtime baseline at 10.15
(Catalina) at the SysRS layer, parallel to SysRS-286 (iOS 13.0) and
SysRS-288 (Android API 28).
Closes the Wave 1.5 traceability-audit deferred-but-optional follow-up.
ID allocation: SysRS-310 (not SysRS-290, which is already allocated to
MVP single-active-server-connection scope); monotonic numbering
preserved.
Cross-references SAD-087, SDD-119, SysRS-286, SysRS-288. Verification:
Review + Platform Test on a macOS 10.15 system. Raising the baseline
(e.g., to 11.0 / Big Sur) requires a DEC entry.
Trace: SysRS v0.9.11, SAD-087, SDD-119.