Add claude config

.claude/commands/build-fix.md

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+# Build and Fix
+
+Incrementally fix Python errors and test failures.
+
+## Workflow
+
+1. Run check: `mypy src/ --ignore-missing-imports` or `pytest -x --tb=short`
+2. Parse errors, group by file, sort by severity (ImportError > TypeError > other)
+3. For each error:
+   - Show context (5 lines)
+   - Explain and propose fix
+   - Apply fix
+   - Re-run test for that file
+   - Verify resolved
+4. Stop if: fix introduces new errors, same error after 3 attempts, or user pauses
+5. Show summary: fixed / remaining / new errors
+
+## Rules
+
+- Fix ONE error at a time
+- Re-run tests after each fix
+- Never batch multiple unrelated fixes