docs: address PR #116 review comments and add v2.1 migration notes

- Update README spec link from v2.0 to v2.1 (fixes #2502418296)
- Fix spacing consistency in ADR-0007 example code (fixes #2502418312)
- Add concise "Changes from v2.0" section to v2.1 spec

All changes improve documentation accuracy and consistency.

Author: synthable

README.md

@@ -209,7 +209,7 @@ Module IDs use a flexible hierarchical format:
 - Examples: `communication/be-concise`, `typescript/error-handling/try-catch`
 - All segments use kebab-case (lowercase with hyphens)
 
-For complete specification details, see [UMS v2.0 Specification](./docs/spec/unified_module_system_v2_spec.md).
+For complete specification details, see [UMS v2.1 Specification](./docs/spec/unified_module_system_v2.1_spec.md).
 
 ## Contributing
 

docs/architecture/adr/0007-simplify-criterion-structure.md

@@ -393,7 +393,7 @@ function renderCriteria(criteria: Criterion[]): string {
 
   // Render uncategorized
   if (uncategorized.length > 0) {
-    sections.push(uncategorized.map(renderItem).join('\n'));
+    sections.push(uncategorized.map(renderItem).join('\n\n'));
   }
 
   // Render categorized groups

docs/spec/unified_module_system_v2.1_spec.md

@@ -1,5 +1,26 @@
 # Specification: The Unified Module System (UMS) v2.1
 
+## Changes from v2.0
+
+### Removed Features
+
+- **ModuleRelationships**: Removed. Will be replaced by Cognitive Hierarchy system and External Graph tool for dependency management.
+- **QualityMetadata component**: Removed. Will be replaced by external registry (design in progress).
+- **ProblemSolution component**: Removed.
+- **ProcessStep fields**: Removed `detail`, `validate`, `when`, `do` fields.
+- **Constraint fields**: Removed `severity`, `when`, `examples`, `rationale` fields.
+- **Criterion fields**: Removed `severity` field.
+
+### Simplified Structures
+
+- **ProcessStep**: Now `string | {step: string, notes?: string[]}` (removed complex validation/conditional fields).
+- **Constraint**: Now `string | {rule: string, notes?: string[]}` (use RFC 2119 keywords in rule text for severity).
+- **Criterion**: Now `string | {item: string, category?: string, notes?: string[]}` (use RFC 2119 keywords in item text for priority).
+
+See Architecture Decision Records (ADRs) in `docs/architecture/adr/` for detailed rationale and migration guidance.
+
+---
+
 ## Migration from v2.0
 
 **Breaking Changes:**