feat: add proposal for cover letter PDF conversion

Add OpenSpec proposal for converting markdown cover letters to PDF format using Swiss business letter standards.

The proposal includes:
- Swiss letter formatting with scrlttr2 and Swiss Norm configuration
- Environment validation for Pandoc and LaTeX
- Comprehensive error handling and user guidance
- Support for Swiss German formatting and address window positioning

This addresses step 7 "Generate PDFs" in the project workflow.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

openspec/changes/add-cover-letter-pdf-conversion/tasks.md

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+# Implementation Tasks
+
+## 1. Template Creation
+- [ ] 1.1 Create Swiss letter LaTeX template at `src/.claude/templates/swiss-letter.tex`
+- [ ] 1.2 Configure scrlttr2 with Swiss Norm (SN) settings
+- [ ] 1.3 Add proper encoding (UTF-8, T1 font encoding) for German characters
+- [ ] 1.4 Implement hyperlinks for email addresses
+- [ ] 1.5 Add Pandoc variable placeholders for all frontmatter fields
+- [ ] 1.6 Add inline comments explaining customizable sections
+- [ ] 1.7 Test template with sample data to ensure proper formatting
+
+## 2. Slash Command Implementation
+- [ ] 2.1 Create command file at `src/.claude/commands/convert-cover-letter.md`
+- [ ] 2.2 Implement cover letter file detection logic
+- [ ] 2.3 Implement environment validation checks (Pandoc, LaTeX)
+- [ ] 2.4 Add platform-specific installation instructions
+- [ ] 2.5 Implement frontmatter parsing and validation
+- [ ] 2.6 Build Pandoc command with correct arguments
+- [ ] 2.7 Execute conversion and capture output
+- [ ] 2.8 Implement error handling for common failure scenarios
+- [ ] 2.9 Add success message with file path output
+
+## 3. Error Handling & Messaging
+- [ ] 3.1 Create clear error message for missing cover letter
+- [ ] 3.2 Create error message for missing required frontmatter fields
+- [ ] 3.3 Create installation guide for Pandoc (apt, brew, winget)
+- [ ] 3.4 Create installation guide for LaTeX packages
+- [ ] 3.5 Add error handling for YAML parsing failures
+- [ ] 3.6 Add error handling for LaTeX compilation failures
+- [ ] 3.7 Add error handling for file permission issues
+- [ ] 3.8 Add timeout handling for long-running conversions
+
+## 4. Testing
+- [ ] 4.1 Test with complete frontmatter and body content
+- [ ] 4.2 Test with minimal required frontmatter only
+- [ ] 4.3 Test with optional enclosures list
+- [ ] 4.4 Test with missing cover-letter.md file
+- [ ] 4.5 Test with invalid YAML frontmatter
+- [ ] 4.6 Test with missing required frontmatter fields
+- [ ] 4.7 Test with special characters (ä, ö, ü, ß) in German text
+- [ ] 4.8 Test environment validation when Pandoc is missing
+- [ ] 4.9 Test environment validation when LaTeX is missing
+- [ ] 4.10 Test error handling for file permission issues
+- [ ] 4.11 Verify Swiss address window positioning with printed output
+- [ ] 4.12 Verify date formatting follows Swiss convention
+
+## 5. Documentation
+- [ ] 5.1 Document required frontmatter structure
+- [ ] 5.2 Document system requirements (Pandoc, LaTeX)
+- [ ] 5.3 Add example cover-letter.md with complete frontmatter
+- [ ] 5.4 Document troubleshooting steps for common errors
+- [ ] 5.5 Add template customization guide
+
+## 6. Integration
+- [ ] 6.1 Update test directory with new command
+- [ ] 6.2 Update test directory with new template
+- [ ] 6.3 Ensure compatibility with existing cover letter generation
+- [ ] 6.4 Verify workflow integration (step 7 in project.md)