Store OKF metadata inside wiki nodes

[humandebri]

Purpose

Promote OKF alignment from Context Pack export compatibility to the internal Kinic Wiki node data model.

Changes

• Add OKF metadata helpers and fixed OKF type handling in wiki_domain.
• Backfill metadata_json with okf_type, resource, source_refs, and trust_level through wiki_store:005_okf_metadata.
• Apply OKF metadata at runtime write boundaries and refresh moved resources.
• Prefer metadata over path inference in Context Pack export.
• Update docs to define Wiki nodes as OKF concepts managed through the VFS.

Validation

• cargo fmt --all
• git diff --check
• ./.local/check.sh

Impact

• Base branch: refactor/four-store-terminology.
• Candid public types are unchanged; existing Node.metadata_json is extended.
• Existing nodes receive metadata backfill and etag/update-log changes through the new store migration.