data dictionary - `dcat-us:describedBy`

[jqnatividad]

The data dictionary should be an extended JSON Schema file, using additionalProperties to capture non-standard JSON Schema elements.

dathere/qsv#2373

Since there is no widely deployed standard for Data Dictionaries, we should create our own.

However, we should still hew closely to related standards like DDI to ensure wider adoption.

[jqnatividad]

This will wait until describegpt has been updated to save Data Dictionaries in jsonschema format.

[jqnatividad]

Deferring this work until qsv issue #2373 lands — i.e., until qsv describegpt produces JSON Schema output natively.

Rationale: building DP+'s data-dictionary-as-extended-JSON-Schema on top of describegpt's current output shape would mean writing (and then throwing away) a conversion layer once qsv emits JSON Schema directly. The cleaner sequence is:

1. qsv#2373 lands → describegpt returns JSON Schema with additionalProperties for non-standard fields
2. DP+ AI suggestions stage consumes that JSON Schema directly (jobs/stages/ai_suggestions.py — currently parses the Dictionary/Description/Tags PascalCase envelope per fix(ai-suggestions): real-qsv schema + CLI flag corrections (PR #301/#302 follow-up) #303)
3. Persist the Data Dictionary as the extended JSON Schema, surface it via dcat-us:describedBy
4. Wire DDI alignment where overlapping

Keeping this issue open and unblocked-pending-upstream. Will revisit when qsv ships the schema output.