Add dotclaude configuration files

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

rules/error-handling.md

@@ -0,0 +1,18 @@
+---
+paths:
+  - "src/api/**"
+  - "src/services/**"
+  - "**/controllers/**"
+  - "**/routes/**"
+  - "**/handlers/**"
+---
+
+# Error Handling
+
+- Use typed/custom error classes with error codes — not generic `Error("something went wrong")`.
+- Never swallow errors silently. Log or rethrow with added context about what operation failed.
+- Handle every rejected promise. No floating (unhandled) async calls.
+- HTTP error responses: consistent shape (e.g., `{ error: { code, message } }`), correct status codes (400 for validation, 401 for auth, 404 for not found, 500 for unexpected).
+- Never expose stack traces, internal paths, or raw database errors in production responses.
+- Retry transient errors (network timeouts, rate limits) with exponential backoff. Fail fast on validation and auth errors — don't retry.
+- Include correlation/request IDs in error logs when available.