docs(skills): improve implement-command guidance

[nkaradzhov]

Summary

Adds recurring guidance to the implement-command skill that kept coming up when wiring new Redis commands:

• Live server first — Step 0 now asks up front for a running instance that has the command and stresses probing every argument branch instead of trusting the spec alone.
• Introducing version — new Step 0 input: which server/module version first ships the command (spec since field, else ask).
• Version-gated tests — Step 3 spreads minimumDockerVersion: [major, minor] into both client and cluster so behavior tests don't run (and fail) on older servers in CI. Arg tests stay ungated.
• @since JSDoc — registry entries get @since <version>.
• RESP2/RESP3 unification — new subsection: RESP3 shape is the source of truth, RESP2 is transformed to match it (3: pass-through, 2: reshape). References HELLO.ts and HGETALL.ts.

Checklist items updated to match.

🤖 Generated with Claude Code

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Note

Low Risk
Documentation-only change to an agent skill file; no production code, tests, or CI behavior is modified.

Overview
Updates .agents/skills/implement-command/SKILL.md so agents follow a tighter workflow when adding Redis commands—no runtime or test code changes.

Step 0 now requires three upfront inputs (spec, live Redis with the command, and the introducing server/module version), with stronger emphasis on probing real replies instead of trusting the spec alone.

New guidance covers RESP2/RESP3: callers see one type—the RESP3 shape—with 3: usually pass-through and 2: reshaping (e.g. HELLO.ts), plus verification over both protocols on the live instance.

Registry JSDoc should include @since from the spec’s since field, and behavior tests should set minimumDockerVersion on both client and cluster (arg/parseArgs tests stay ungated). The completion checklist and spec-mapping table are aligned with these rules.

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