feat(concept): add comprehensive stereotype and vocabulary documentation

Add dedicated pages for Outcome Stereotype, Use Case Stereotype, and
Concept Vocabulary with full diagrams, tabs, and cross-references.

Changes:
- Restructure use-case.md into use-case/ directory with index.md
- Create use-case-stereotype.md with organization-defined stereotypes
- Enhance outcome-stereotype.md with tabs (Business, Common Stereotypes,
  Best Practices, Relationships, Ontology)
- Create concept-vocabulary.md explaining SKOS extension with
  Concept-to-Terms one-to-many relationship
- Add new diagrams: uctm-outcome-stereotype.puml,
  uctm-concept-vocabulary.puml
- Update all existing diagrams to include OutcomeStereotype and
  ConceptVocabulary with hyperlinks
- Fix all broken links after use-case restructuring (27 files updated)
- Add .pages.yaml navigation for new directory structures

All pages follow consistent format with tabs, diagrams using <object>
tags for clickable links, and comprehensive ontology sections.

Author: jgeluk

docs/concept/.pages.yaml

@@ -1,7 +1,7 @@
 title: Concepts
 nav:
   - use-case-tree.md
-  - use-case.md
+  - use-case
   - persona
   - story.md
   - concept

docs/concept/concept/.pages.yaml

@@ -1,4 +1,5 @@
 title: Concept
 nav:
   - index.md
+  - Concept Vocabulary: concept-vocabulary.md
   - Story/Concept Relationship: story-concept-relationship.md