Archive import drops standard IMDF relationship semantics

[jillesvangurp]

Summary

Archive import only interprets relationship features when they use a custom category="contains" + references[] format, and ignores standard IMDF relationship semantics.

Evidence

• src/lib/imdf/archiveImport.ts:372 explicitly filters relationships to category === "contains" and properties.references.
• src/lib/imdf/archiveImport.ts:375 assumes references[0]/references[1] parent-child shape.
• src/lib/imdf/archiveImport.ts:294-301 parses origin_id / intermediary_id / destination_id from non-relationship collections, but relationship collection itself is not mapped into route relations.

Why this is a bug

IMDF relationship features carrying route/traversal semantics are silently dropped during import. This loses connectivity semantics and prevents faithful round-trip behavior.

Reproduction

1. Import an IMDF archive containing relationship features with origin/intermediary/destination semantics.
2. Check imported feature metadata and routing/containment state.
3. Observe that those relationships are ignored unless they match the custom contains + references shape.

Expected

• Parse relationship collection according to IMDF relationship properties.
• Preserve relationship semantics during import (not only containment overrides).

Impact

Import is lossy for real-world IMDF datasets and cannot preserve relationship intent.