fix: Remove unsupported style separators from Mermaid subgraph declarations

[abrichr]

Summary

• Removed :::futureBlock style separator from the ProcessMining subgraph declaration
• Removed :::safetyBlock style separator from the SafetyGate subgraph declaration

GitHub's Mermaid renderer doesn't support the ::: style separator on subgraph declarations, causing the following parse error:

Parse error on line 34:
...ng["Process Mining"]:::futureBlock
-----------------------^
Expecting 'SEMI', 'NEWLINE', 'EOF', got 'STYLE_SEPARATOR'

The individual nodes within these subgraphs still retain their :::future class styles, so visual differentiation of future features is preserved.

Test plan

• Verify the Mermaid diagram renders correctly on GitHub after merge

🤖 Generated with Claude Code