fix: wrap repo service errors in UserError for cleaner output

[stack72]

• Wrap "repository already initialized" and "not a swamp repository" errors in UserError to suppress stack traces
• These are expected user-facing conditions where the stack trace is noise

Test plan

• deno check passes
• deno run test src/domain/repo/ passes

[github-actions]

Review Summary

This PR correctly wraps repository initialization errors in UserError to suppress stack traces for expected user-facing conditions. The changes align well with the established error handling pattern in this codebase.

Analysis

Code Quality: ✅

• Clean, minimal change that follows existing patterns
• UserError is already used throughout the codebase (16 files) for similar purposes
• The error handling in src/presentation/output/error_output.tsx:32-33 properly detects UserError instances and suppresses stack traces

TypeScript Compliance: ✅

• No any types
• Uses named imports correctly
• Type-safe implementation

Test Coverage: ✅

• Existing tests at repo_service_test.ts:115-129 and repo_service_test.ts:183-194 will continue to pass because UserError extends Error
• The assertRejects calls check for Error type and error message content, both of which are preserved

DDD Principles: ✅

• UserError is appropriately defined in the domain layer (src/domain/errors.ts)
• The separation between internal errors (show stack) and user-facing errors (no stack) is a valid domain concept

Security: ✅

• No security concerns - this change actually improves UX by reducing noise in error output

Suggestions (Non-blocking)

1. Consider stronger test assertions: The tests could be updated to assert UserError specifically instead of Error to document the intended behavior more explicitly. However, this is optional since the current tests correctly verify the error messages.

LGTM!