chore: Add SDD skills

.agents/skills/research/SKILL.md

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+---
+name: research
+description: Investigate a question against high-trust primary sources and capture the findings as a Markdown file in the repo. Use when the user wants a topic researched, docs or API facts gathered, or reading legwork delegated to a background agent.
+---
+
+Spin up a **background agent** to do the research, so you keep working while it reads.
+
+Its job:
+
+1. Investigate the question against **primary sources** (official docs, source code, specs, first-party APIs), not a secondary write-up of them. Follow every claim back to the source that owns it.
+2. Write the findings to a single Markdown file, citing each claim's source.
+3. Save it where the repo already keeps such notes; match the existing convention, and if there is none, put it somewhere sensible and say where.

.agents/skills/research/agents/openai.yaml

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+interface:
+  display_name: "Research"
+  short_description: "Research from high-trust sources"