Read spec and release graph data from published Populace bundles

[MaxGhenis]

#9 checks in a generated static graph from current Populace and Ledger source contracts. Once Populace release bundles publish spec artifacts, the site should render those artifacts by release id instead of relying on source-code extraction.

Need:

• Release bundles publish spec graph, target registry, source coverage, lineage, target weights, and gate-result JSON artifacts.
• The site loads those artifacts by release id and shows source provenance.
• The current source-code graph remains available as a development fallback until bundle artifacts exist.

Acceptance criteria:

• No hand-authored graph JSON is required for published releases.
• A release id can select the matching graph, target registry, and diagnostics.
• Missing bundle artifacts degrade visibly rather than showing stale data.