v0.3.0

• Upgrade the HigherGraphen dependency from 0.5.0 to 0.7.1 and consume the
  higher-graphen-* crates from crates.io instead of a ../higher-graphen
  path checkout (CI no longer clones the upstream repo).
• Back projection-loss metrics with HigherGraphen's measure_projection_loss
  kernel and route untraced/empty output through it, retiring the hand-rolled
  loss heuristic. Behavior change: an all-untraced (Text) projection now
  reports risk_severity "medium" (was "low") with explicit
  source_trace_missing / unsupported_loss_metric review signals.
• Read gluing / difference / overlap classifications via typed HigherGraphen
  enums (GluingResult / DifferenceSeverity / OverlapWitnessKind) instead of
  matching serialized wire-name strings (output unchanged).
• Populate the lift Morphism's typed lost_structure from the source
  boundary's extraction_loss / excluded_summary, replacing the parallel
  untyped loss_claims blob.
• Enrich obstruction counterexamples with structural witness assignments
  (from_cell_id / to_cell_id / route_path / http_methods).
• Internal: split oversized modules so every source file satisfies the
  400-line cap (behavior-preserving; public APIs and golden output unchanged).