fix: mark ripgrep no-match as completed

[kocaemre]

Summary

• Treat standalone rg/ripgrep commands that exit 1 with no output as completed ACP tool calls instead of failures.
• Reuse the status mapping for both live command completion events and session-history replay.
• Keep diagnostics, exit code 2, and compound shell commands as failures.

Closes #468.

Test Plan

• npm test -- src/__tests__/CodexACPAgent/command-execution-status.test.ts
• npm run typecheck
• npm run build
• npm test
• git diff --check