Add research skill for delegated primary-source investigation

[bracyw]

What

Adopt Matt Pocock's research skill: spin up a background agent to investigate a question against primary sources (official docs, source code, specs, first-party APIs), then leave a single cited markdown file where the repo keeps such notes.

Why

• It's a wayfinder ticket type (research/AFK), so wayfinder adoption depends on it.
• It fills a dangling reference in the journal work (Journal skill: full export flow-picker (to-issues, to-prd, grill-with-docs, research) #680/#677 - add journal skill for local capture and delegated export #681), which currently treats "research" as a plain docs write because no research skill exists.

Acceptance criteria

• .claude/skills/research/SKILL.md added, Argos-adapted (saves notes matching the repo convention)
• Skill loads and is reachable

Part of the Matt-Pocock-skills sync begun in #683/#684.