feat: add --json option to search command

[s21v1d9p]

This PR adds a --json option to the search command to output results in JSON format. Fixes #46.

---

Note

Adds a --json flag to mgrep search to output raw JSON for search and answer responses, with accompanying tests.

• CLI / Search Command
  • Add --json option to src/commands/search.ts.
  • When --json is set:
    • For search: print store.search results as JSON.
    • For answer: print store.ask results as JSON.
  • Preserve existing formatted output when --json is not used.
• Tests (test/test.bats)
  • Add tests for --json output, --json --answer, and --json with no results.

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