feat: 新增 jsc-matt 外掛，收錄 Matt Pocock 全套技能，指令為 /jsc-matt:*

- 改編自 mattpocock/skills 1.2.3（MIT），含 engineering 與 productivity 共 25 個技能
- 技能間的呼叫名稱一律加上 jsc-matt: 前綴
- marketplace 與 README 補上 jsc-matt

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

plugins/jsc-matt/skills/productivity/README.md

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+# Productivity
+
+General workflow tools, not code-specific.
+
+## User-invoked
+
+Reachable only when you type them (Claude Code: `disable-model-invocation: true`; Codex: `policy.allow_implicit_invocation: false` in `agents/openai.yaml`).
+
+- **[grill-me](./grill-me/SKILL.md)**: Get relentlessly interviewed about a plan or design until every branch of the design tree is resolved.
+- **[handoff](./handoff/SKILL.md)**: Compact the current conversation into a handoff document so another agent can continue the work.
+- **[teach](./teach/SKILL.md)**: Teach the user a new skill or concept over multiple sessions, using the current directory as a stateful teaching workspace.
+- **[to-questionnaire](./to-questionnaire/SKILL.md)**: Turn a decision you can't answer alone into a Markdown questionnaire for the one person who can (filled in async, or together over a meeting).
+- **[wait-what](./wait-what/SKILL.md)**: Fire this the moment a message doesn't land. The agent re-pitches it with the context you're missing, in plain English, using your `CONTEXT.md` vocabulary.
+
+## Model-invoked
+
+Model- or user-reachable (rich trigger phrasing so the model can reach for them).
+
+- **[grilling](./grilling/SKILL.md)**: Interview the user relentlessly about a plan, decision, or idea until every branch of the design tree is resolved.
+- **[writing-for-agents](./writing-for-agents/SKILL.md)**: Writing documents for agents: skills, AGENTS.md/CLAUDE.md, and any doc an agent reaches by a pointer.