Replace inlined path normalisation with _norm_source_file (the same function
that builds node source_file keys) so prune_set and node attrs are normalised
identically. resolve() on root handles symlinked scan roots. Keep both raw and
normalised forms in prune_set so nodes with absolute source_file also match.
Add edge pruning and Windows backslash path tests per Opus review.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>