Investigate "agent-first" CLIs and document their use across skills

## Background

Spun off from #29 ("CLI Speed Tools" PR), where the discussion surfaced that "human-fast" tools (`rg`, `fd`, `bat`, `eza`, `dust`, ...) optimize for human ergonomics, which is not always the same as "agent-friendly". For an agent that consumes CLI output as text and pays a per-tool-call cost, the properties that matter most are different.

Worth tracking this independently, since #29 may end up scoped only to the project's `CLAUDE.md` and the agent-first angle is broader: it should inform guidance inside the existing skills, not just one document in this repo.

## What "agent-first" means here

Tools designed to be driven by an LLM or an agent, rather than by a human at a terminal. The properties that matter:

- Structured output by default or via a flag (`--json`, `--ndjson`, `-o json`).
- Stable, parseable exit codes and machine-readable error messages.
- Idempotent or dry-run modes for safe exploration.
- No interactive prompts, or a clean non-interactive flag.
- Predictable, deterministic output across runs (no random ordering, no spinners in the pipe).
- Low startup overhead (matters when an agent issues many short calls).

## Tools that already fit the shape

Non-exhaustive starting list:
- `gh` (GitHub CLI), first-class `--json` and `--jq`.
- `jq`, designed for piping structured data.
- `kubectl -o json` / `-o yaml`.
- `actionlint`, predictable diagnostics with clear exit codes.
- `shellcheck -f json`.

Worth researching:
- Newer CLIs that explicitly frame themselves as agent-friendly or LLM-friendly.
- Whether `nushell` patterns transfer (everything is structured by default).
- Which tools listed in #29 also have a usable structured-output path (e.g. `rg --json`, `fd --print0`, `delta` exit codes).

## Proposed scope

1. Survey: which CLIs in current use across the skills have first-class structured output, deterministic behavior, and clean non-interactive modes.
2. Recommend defaults per skill where it matters:
- `debugging-and-error-recovery` and `context-engineering` for search and read.
- `git-workflow-and-versioning` for diff and history.
- `code-review-and-quality` for static analysis output.
- `ci-cd-and-automation` for pipeline linting.
3. Produce a `references/agent-first-clis.md` and link from the relevant skills, rather than adding a new top-level skill.

## Open questions

- Should this live as a new skill or only as a reference cross-linked from existing skills?
- Where does the line between "fast for humans" and "good for agents" sit, and which tools satisfy both?
- Should there be a small `command -v` preflight pattern shared across skills that depend on optional tools?

Happy to take this on once direction is agreed.