Read GitHub Projects v2 boards as a source scope #40

Graphle could load a whole Projects v2 board by pasting its URL (github.com/orgs/<login>/projects/<n> or users/...), skipping draft items. The GitHub issues source has no project scope: parseScope accepts github:owner and github:owner/repo only and queries.ts selects no projectsV2, so the web app in #39 cannot offer it.

What it needs: a project scope form in graph-source-github-issues (for example github:owner/projects/<n>, read through organization.projectV2 or user.projectV2 items, issue items as bound activities, drafts as gaps or skipped), and then a line in graph-web's readScopeInput that turns a pasted project URL into that scope. The web app's scope picker already reads github.com links for owners and repositories.

Deferred because it is an adapter change with its own fixtures and conformance run, outside the web app PR. Listed as L-07 and L-08 in the Graphle parity inventory for phase 7.