feat(ci): add markdownlint-cli2 for consistent markdown formatting

Add automated markdown linting to ensure consistent formatting across
all markdown files in the repository.

Changes:
- Add .markdownlint-cli2.jsonc configuration
- Create .github/workflows/lint.yml for CI/CD integration
- Fix all 908 existing markdown errors across 27 files
- Enforce ATX-style headings and asterisk emphasis
- Set consistent 2-space list indentation

This prevents markdown errors after project initialization and
maintains high documentation quality standards.

CHANGELOG.md

@@ -63,7 +63,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - New `/clarify` command template to surface up to 5 targeted clarification questions for an existing spec and persist answers into a Clarifications section in the spec.
 - New `/analyze` command template providing a non-destructive cross-artifact discrepancy and alignment report (spec, clarifications, plan, tasks, constitution) inserted after `/tasks` and before `/implement`.
-	- Note: Constitution rules are explicitly treated as non-negotiable; any conflict is a CRITICAL finding requiring artifact remediation, not weakening of principles.
+  - Note: Constitution rules are explicitly treated as non-negotiable; any conflict is a CRITICAL finding requiring artifact remediation, not weakening of principles.
 
 ## [0.0.16] - 2025-09-22
 
@@ -140,7 +140,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Updated command instructions in the CLI.
 - Cleaned up the code to not render agent-specific information when it's generic.
 
-
 ## [0.0.6] - 2025-09-17
 
 ### Added
@@ -166,4 +165,3 @@ N/A
 ### Changed
 
 N/A
-