feat(log-query): add jq: filter syntax to improve JSON log readability (JMESPath to follow)

[sarub0b0]

Summary

To improve the readability of JSON logs, this PR adds a jq:<expr> filter syntax to the log query input form. This allows extracting specific fields and restructuring output inline in the query.
JMESPath will be added in a subsequent PR (jmespath:<expr>).

Background

As noted in the issue, raw JSON logs can be verbose and make it hard to quickly reach the needed information during operations. Allowing a filter expression directly in the query enables on-the-fly transformation into a more readable view.

Scope (this PR)

• New syntax: jq:<expr>

  • If a log line is valid JSON, apply <expr> and render the result.
  • For non-JSON lines or evaluation failures, show the raw log with error context to aid debugging.

• Works alongside existing query terms such as log: / !log:, pod:, container:.

• Help: add jq: documentation and examples to the query help.

• Documentation: update README with jq filter usage and examples.

Usage examples

# Example 1: show only the message
pod:api log:error jq:.message

# Example 2: restructure to {ts, level, msg}
pod:api jq:'{ts:.time, level:.level, msg:.msg}'

Compatibility

• Default behavior is unchanged unless jq: is specified.
• No breaking changes to existing text filters or resource selectors.

Tests

• Parser: jq: tokenization, quoting/escaping, rule when multiple jq: are provided (last one wins).
• Filter compilation: valid/invalid jq expressions, error handling, combination with other filters.
• Runtime: extraction/restructuring, invalid expressions, non-JSON lines, jq evaluation errors, pretty print combinations, multi-value queries.
• Help: jq: entry appears correctly in help dialog.

Added 16 comprehensive tests covering parser, compilation, and log rendering scenarios.

Future work (separate PRs)

• jmespath:<expr> support.