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.

templates/commands/plan.md

@@ -43,7 +43,8 @@ You **MUST** consider the user input before proceeding (if not empty).
    - For each integration → patterns task
 
 2. **Generate and dispatch research agents**:
-   ```
+
+   ```text
    For each unknown in Technical Context:
      Task: "Research {unknown} for {feature context}"
    For each technology choice:
@@ -84,4 +85,3 @@ You **MUST** consider the user input before proceeding (if not empty).
 
 - Use absolute paths
 - ERROR on gate failures or unresolved clarifications
-