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/tasks-template.md

@@ -1,4 +1,5 @@
 ---
+
 description: "Task list template for feature implementation"
 ---
 
@@ -12,11 +13,13 @@ description: "Task list template for feature implementation"
 **Organization**: Tasks are grouped by user story to enable independent implementation and testing of each story.
 
 ## Format: `[ID] [P?] [Story] Description`
+
 - **[P]**: Can run in parallel (different files, no dependencies)
 - **[Story]**: Which user story this task belongs to (e.g., US1, US2, US3)
 - Include exact file paths in descriptions
 
 ## Path Conventions
+
 - **Single project**: `src/`, `tests/` at repository root
 - **Web app**: `backend/src/`, `frontend/src/`
 - **Mobile**: `api/src/`, `ios/src/` or `android/src/`
@@ -78,7 +81,7 @@ Examples of foundational tasks (adjust based on your project):
 
 ### Tests for User Story 1 (OPTIONAL - only if tests requested) ⚠️
 
-**NOTE: Write these tests FIRST, ensure they FAIL before implementation**
+> **NOTE: Write these tests FIRST, ensure they FAIL before implementation**
 
 - [ ] T010 [P] [US1] Contract test for [endpoint] in tests/contract/test_[name].py
 - [ ] T011 [P] [US1] Integration test for [user journey] in tests/integration/test_[name].py
@@ -246,6 +249,3 @@ With multiple developers:
 - Commit after each task or logical group
 - Stop at any checkpoint to validate story independently
 - Avoid: vague tasks, same file conflicts, cross-story dependencies that break independence
-
-
-