Nebula 3.0.31

Changes since nebula-v3.0.30:

• d5d4b509 Keep one verified Core rollback snapshot after promotion (#869)
• cb729000 Give scheduled Butler full Assistant work authority and remove investigation caps (#868)
• 438a0f1f Document Nebula system architecture (#867)
• 6c1142f1 Make agent planning advisory across providers and harnesses (#865)
• a6c9680d Group Butler-initiated chats under Butler in conversations (#859)
• 99556f80 Add Core-enforced Grok plans and Butler same-chat handoff (#864)
• 137feef5 Allow Core plans on existing unrestricted Codex profiles (#863)
• 4464e5f4 Enable Core formal task plans for managed Codex (#861)
• a7d46039 Honor saved harness effort when resuming Core-owned goals
• fc6599aa Preserve Git CA for managed harness workers (#860)
• 93baa6c1 Preserve user home for native hook Git credentials (#858)
• 4bf53fa2 Preserve Butler recovery attempts and route by usable capacity