[Obsidian] Define the companion plugin scope

[Longfellow1]

Background

KeyPulse already writes Markdown into Obsidian. A future companion plugin should stay thin and avoid becoming a second product.

Task

Draft the minimum useful Obsidian companion plugin scope.

Acceptance criteria

• Plugin scope explains what belongs in Obsidian and what belongs in the Mac app / CLI
• Plugin can open today's KeyPulse daily note
• Plugin can show recent review items
• Plugin can expose template configuration or links to templates
• Plugin does not duplicate the capture daemon or privacy pipeline