feat(forage): unify forage items

Summary

• Flatten Forage into one queue for feature requests, bug reports, feedback, GitHub issues, and Grafana alerts with filters, search, pagination, feeds, and detail routes.
• Add manual forage item types, author-only item editing, and comments for manual items while fetching GitHub issue comments on demand.
• Update navigation, Slack capture links, OpenGraph/feed metadata, seeds, tests, and docs for the unified Forage model.

Testing

• mix format --check-formatted
• mix compile --warnings-as-errors
• mix test
• git diff --check

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