chore: consolidate .opencode/ pass-throughs into decision.md
Delete five thin wrappers (deciduous.md, sync-graph.md, version-check.ts,
SKILL.md, deciduous.ts) that restate content already in commands/decision.md
or AGENTS.md. Fold commands/work.md and commands/document.md into
decision.md as ## Workflow: /work and ## Workflow: /document subsections so
decision.md is the single reference for all workflow details. Drop the now-
dead SKILL.md pointer from the AGENTS.md Task flow preamble.
Closes #6
https://claude.ai/code/session_01Bc9nxmsXYG6cgiwcb5GZP1