feat: add PlanarGraphAnalyzer — planarity testing, face enumeration, dual graph, Kuratowski detection (#32)

Implements comprehensive planar graph analysis:
- Planarity testing via Euler bound + K5/K3,3 minor detection with
  exhaustive contraction for small graphs and multi-strategy heuristics
- Face enumeration using combinatorial planar embeddings with
  force-directed layout for cyclic neighbor ordering
- Dual graph construction from face-adjacency relationships
- Kuratowski subgraph extraction (K5 or K3,3 subdivision certificates)
- Full PlanarityReport with genus estimation and formatted output
- Triangle-free graph bound (E <= 2V-4) for tighter rejection

Tested against: empty, single vertex/edge, triangle, K4 (planar),
K5/K3,3/Petersen (non-planar), paths, cycles, wheels, stars, trees,
octahedron, cube graph, disconnected graphs. 47 tests, all passing.

Author: sauravbhattacharya001