docs(book): Add ADR-002 for topology without hardcoded node counts

Architecture Decision Record documenting topology/basis separation (292 lines):

- Explains decision to remove node counts from topology types
- Documents topology = pure geometry, basis determines node count
- Shows old Code Aster anti-pattern (TRIA3, TRIA6, QUAD4, QUAD8)
- Describes new design: Triangle + Lagrange{Triangle, P}
- Rationale: mathematical correctness, separation of concerns
- Enables edge/face DOFs (Nédélec, Raviart-Thomas)
- Eliminates combinatorial explosion (8 topologies vs hundreds)
- Consequences: extensible, correct, but breaking change
- Implementation strategy and migration plan
- Includes proper YAML front matter for book chapter

docs/book/adr-002-topology-without-node-count.md

@@ -1,8 +1,18 @@
-# ADR 002: Topology Types Without Hardcoded Node Counts
-
-**Date:** November 9, 2025  
-**Status:** Accepted  
-**Supersedes:** ADR 001 (partial - corrects topology design)
+---
+title: "ADR 002: Topology Types Without Hardcoded Node Counts"
+description: "Architecture decision to separate topology (geometry) from node count (determined by basis)"
+date: "November 9, 2025"
+author: "Jukka Aho"
+categories: ["architecture", "design-decision", "adr"]
+keywords: ["topology", "basis", "lagrange", "separation-of-concerns", "node-count"]
+audience: "researchers"
+level: "advanced"
+type: "adr"
+series: "The JuliaFEM Book"
+chapter: 3
+status: "accepted"
+supersedes: "ADR 001 (partial)"
+---
 
 ## Context