feat: add local contribution dashboard

[shaoohh]

Summary

This PR adds an openmeta dashboard command that serves a fixed contribution dashboard template backed by local OpenMeta state.

It includes:

• a fixed dashboard asset bundle under dashboard/
• a lightweight local server for static assets and dashboard data
• /api/dashboard and /api/dashboard/refresh
• local snapshot materialization into dashboard-data.json
• a real-data adapter for proof-of-work / inbox / repo-memory / artifacts
• focused tests for command wiring, server behavior, and data adaptation

Why

The goal is to make contribution history easier to inspect and review:

• what was done
• which projects saw contribution activity
• which projects are better candidates for deeper follow-up

My own local data is still sparse, so I want reviewers to run this against their own local OpenMeta state and judge the page structure and signal quality.

Reviewer Notes

bun install
bun run build
openmeta dashboard