Function applyTombstones

Remove tombstoned nodes (and their subtrees) from a composed node map.

• Nodes whose strongest ifclite::deleted opinion is true are removed.
• Their descendants (reachable through children) are removed with them.
• References to removed nodes are dropped from surviving parents.
• The ifclite::deleted marker itself is stripped from survivors so the composed state is clean for extractors and export.

The input map is mutated in place (composition owns these structures) and returned for convenience.