[RFE] Parse and expose user-defined metadata

[pmatulis]

Display pages (nodes in a graph) that contain user-defined metadata (maybe implemented in the form of a comment).

Use cases:

1. A page's content requires a review based on severity. The metadata can be Review1, Review2, Review3.
2. A page is missing a specific kind of data like doc requirements. The metadata can be MissingRV (for missing required verification step).
3. A page has met all doc requirements. The metadata can be DocApproved.
4. A page has received a significant content review and receives metadata based on the date like Reviewed-2025-03-15. A few degrees of last-updated times can then be exposed:
   • more than 2 years ago (red)
   • between 1 and 2 years (amber)
   • less than 1 year (green)

Each use case would have its data displayed using its own selectable layer.