feat: add case + party CRUD with case events (Phase 1B)

.claude/agents/coder.md

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+# Coder Agent
+
+Implementation-focused agent for writing and refactoring code.
+
+## Instructions
+
+- Follow existing patterns in the codebase
+- Write minimal, focused code
+- Run tests after changes
+- Commit incrementally with descriptive messages
+
+## Tools
+
+All tools available.