chore: label taxonomy normalization and enforcement

[ggfevans]

Summary

Normalize label taxonomy and add lightweight enforcement to prevent drift in issue classification.

Problem

Current labels include taxonomy drift (e.g. area:data-schema-persistance typo), and many issues are missing expected classification labels (especially area labels).

Acceptance Criteria

• Resolve misspelled/legacy label names with a migration mapping.
• Backfill open issues so canonical labels are applied consistently.
• Define minimum label standards for implementation-ready issues (type + area + size + priority).
• Add an automated check or maintainer checklist step to prevent recurrence.

Notes

• Preserve history by relabeling existing issues rather than losing context.
• Keep enforcement pragmatic; avoid blocking triage for early idea capture.