Fusion: port SIN-Code-Grill-Me-Skill to native sin-code grill

[Delqhi]

Goal

Port the SIN-Code-Grill-Me-Skill conversation logic into a native sin-code grill subcommand, then fuse the bundled skill with the native implementation and deprecate the external Python MCP server.

Background

• SIN-Code-Grill-Me-Skill is an external Python MCP server (38 KB) that performs adversarial design-review interviews.
• SIN-Code/skills/sin-grill-me currently only contains a bundled SKILL.md doc.
• There is no native sin-code grill command yet.

Why Fusion Makes Sense After a Native Command

Once grill-me is implemented as a native sin-code grill subcommand:

• No separate Python runtime / MCP server is required.
• The bundled SKILL.md can document the native command.
• The external SIN-Code-Grill-Me-Skill can be deprecated and archived.

Native Command Design Ideas

• sin-code grill start — begin a grilling session on a topic/plan.
• sin-code grill next — ask the next adversarial question.
• sin-code grill answer — record the user's answer and resolve a decision.
• sin-code grill status — show resolved and unresolved decision branches.
• sin-code grill synthesize — produce a summary of decisions, assumptions, and open questions.
• Store sessions in the SQLite session/ledger DB for multi-turn continuity.

Tasks

• Implement cmd/sin-code/grill_cmd.go with the subcommands above.
• Add a backing package (e.g. cmd/sin-code/internal/grill) for session/decision-tree logic.
• Port the anti-patterns and question catalog from SIN-Code-Grill-Me-Skill/SKILL.md.
• Update SIN-Code/skills/sin-grill-me/SKILL.md to document the native sin-code grill command.
• Mark SIN-Code-Grill-Me-Skill repository as deprecated in its README and archive it after one release cycle.
• Update mcpclient/registry.go and skillmgr.KnownSkills() to remove the grillme external server entry (or mark it deprecated).
• Add lifecycle: native to skills/sin-grill-me/SKILL.md.

Acceptance Criteria

• sin-code grill --help exposes all subcommands.
• A full grilling session can be started, answered, and synthesized without the external MCP server.
• python3 scripts/validate_skill.py --all-bundled --strict passes for sin-grill-me.
• The external SIN-Code-Grill-Me-Skill repo shows a deprecation notice.

[Delqhi]

Closed: shipped in PR #220 (feat(grill): native sin-code grill CLI, issue #141 fusion). 5 subcommands: start, next, answer, status, synthesize. 14 race-clean tests in cmd/sin-code/internal/grill/. Replaces the external SIN-Code-Grill-Me-Skill Python MCP server (38 KB). v0 ships JSON storage; SQLite session storage is a v1 follow-up.