fix(collections): enable markdownlint for collections/*.collection.md

- remove collections/*.collection.md from .markdownlint-cli2.jsonc ignores
- add H1 titles, Included Artifacts headings, and blockquote previews to all 13 collection manifests
- replace em-dashes with hyphens in design-thinking instructions/prompts frontmatter and in-scope docs
- update Prepare-Extension.ps1 generator to emit Included Artifacts header
- regenerate plugins/**/README.md for all 13 collections

Closes #1341

🧹 - Generated by Copilot

Co-authored-by: WilliamBerryiii <williamberry@github.com>

Author: 2 people

.github/instructions/design-thinking/dt-curriculum-01-scoping.instructions.md

@@ -1,5 +1,5 @@
 ---
-description: 'DT Curriculum Module 1: Scope Conversations — concepts, techniques, checks, and exercises'
+description: 'DT Curriculum Module 1: Scope Conversations - concepts, techniques, checks, and exercises'
 applyTo: '**/.copilot-tracking/dt/**/curriculum-01*'
 ---
 

.github/instructions/design-thinking/dt-curriculum-02-research.instructions.md

@@ -1,5 +1,5 @@
 ---
-description: 'DT Curriculum Module 2: Design Research — concepts, techniques, checks, and exercises'
+description: 'DT Curriculum Module 2: Design Research - concepts, techniques, checks, and exercises'
 applyTo: '**/.copilot-tracking/dt/**/curriculum-02*'
 ---
 

.github/instructions/design-thinking/dt-curriculum-03-synthesis.instructions.md

@@ -1,5 +1,5 @@
 ---
-description: 'DT Curriculum Module 3: Synthesis — concepts, techniques, checks, and exercises'
+description: 'DT Curriculum Module 3: Synthesis - concepts, techniques, checks, and exercises'
 applyTo: '**/.copilot-tracking/dt/**/curriculum-03*'
 ---
 

.github/instructions/design-thinking/dt-curriculum-04-brainstorming.instructions.md

@@ -1,5 +1,5 @@
 ---
-description: 'DT Curriculum Module 4: Brainstorming — concepts, techniques, checks, and exercises'
+description: 'DT Curriculum Module 4: Brainstorming - concepts, techniques, checks, and exercises'
 applyTo: '**/.copilot-tracking/dt/**/curriculum-04*'
 ---
 

.github/instructions/design-thinking/dt-curriculum-05-concepts.instructions.md

@@ -1,5 +1,5 @@
 ---
-description: 'DT Curriculum Module 5: User Concepts — concepts, techniques, checks, and exercises'
+description: 'DT Curriculum Module 5: User Concepts - concepts, techniques, checks, and exercises'
 applyTo: '**/.copilot-tracking/dt/**/curriculum-05*'
 ---
 

.github/instructions/design-thinking/dt-curriculum-06-prototypes.instructions.md

@@ -1,5 +1,5 @@
 ---
-description: 'DT Curriculum Module 6: Low-Fidelity Prototypes — concepts, techniques, checks, and exercises'
+description: 'DT Curriculum Module 6: Low-Fidelity Prototypes - concepts, techniques, checks, and exercises'
 applyTo: '**/.copilot-tracking/dt/**/curriculum-06*'
 ---
 

.github/instructions/design-thinking/dt-curriculum-07-testing.instructions.md

@@ -1,5 +1,5 @@
 ---
-description: 'DT Curriculum Module 7: High-Fidelity Prototypes — concepts, techniques, checks, and exercises'
+description: 'DT Curriculum Module 7: High-Fidelity Prototypes - concepts, techniques, checks, and exercises'
 applyTo: '**/.copilot-tracking/dt/**/curriculum-07*'
 ---
 

.github/instructions/design-thinking/dt-curriculum-08-iteration.instructions.md

@@ -1,5 +1,5 @@
 ---
-description: 'DT Curriculum Module 8: User Testing — concepts, techniques, checks, and exercises'
+description: 'DT Curriculum Module 8: User Testing - concepts, techniques, checks, and exercises'
 applyTo: '**/.copilot-tracking/dt/**/curriculum-08*'
 ---
 

.github/instructions/design-thinking/dt-curriculum-09-handoff.instructions.md

@@ -1,5 +1,5 @@
 ---
-description: 'DT Curriculum Module 9: Iteration at Scale — concepts, techniques, checks, and exercises'
+description: 'DT Curriculum Module 9: Iteration at Scale - concepts, techniques, checks, and exercises'
 applyTo: '**/.copilot-tracking/dt/**/curriculum-09*'
 ---
 

.github/instructions/design-thinking/dt-curriculum-scenario-manufacturing.instructions.md

@@ -1,5 +1,5 @@
 ---
-description: 'Manufacturing reference scenario for DT learning — factory floor improvement project used across all 9 curriculum modules'
+description: 'Manufacturing reference scenario for DT learning - factory floor improvement project used across all 9 curriculum modules'
 applyTo: '**/.copilot-tracking/dt/**/curriculum-*'
 ---