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>

src/.claude/templates/swiss-letter.tex

@@ -0,0 +1,120 @@
+% Swiss Business Letter Template for Pandoc
+% This template follows Swiss standards (SN) for business correspondence
+% Compatible with KOMA-Script scrlttr2 class
+
+\documentclass[
+  fontsize=11pt,
+  paper=a4,
+  parskip=half,           % Half line spacing between paragraphs
+  fromalign=right,        % Sender address aligned right
+  fromphone,              % Include phone number
+  fromemail,              % Include email address
+  version=last            % Use latest KOMA-Script features
+]{scrlttr2}
+
+% ==================== ENCODING & FONTS ====================
+% UTF-8 input encoding for special characters (ä, ö, ü, ß)
+\usepackage[utf8]{inputenc}
+% T1 font encoding for proper hyphenation and special characters
+\usepackage[T1]{fontenc}
+
+% ==================== HYPERLINKS ====================
+% Enable clickable email links in PDF
+\usepackage{hyperref}
+\hypersetup{
+  colorlinks=true,
+  urlcolor=black,
+  pdfborder={0 0 0}
+}
+
+% ==================== PANDOC COMPATIBILITY ====================
+% Define tightlist command for Pandoc-generated lists
+\providecommand{\tightlist}{%
+  \setlength{\itemsep}{0pt}\setlength{\parskip}{0pt}}
+
+% ==================== SWISS LETTER CONFIGURATION ====================
+% Load Swiss Norm (SN) for proper address window positioning
+% This ensures the recipient address fits in standard Swiss envelope windows
+\LoadLetterOption{SN}
+
+% ==================== SENDER INFORMATION ====================
+% Customize these fields by editing the markdown frontmatter
+\setkomavar{fromname}{$from.name$}
+\setkomavar{fromaddress}{$from.street$\\$from.city$}
+
+$if(from.phone)$
+\setkomavar{fromphone}{$from.phone$}
+$endif$
+
+$if(from.email)$
+% Email is rendered as a clickable hyperlink
+\setkomavar{fromemail}{\href{mailto:$from.email$}{$from.email$}}
+$endif$
+
+% ==================== LETTER METADATA ====================
+$if(subject)$
+\setkomavar{subject}{$subject$}
+$endif$
+
+$if(date)$
+\setkomavar{date}{$date$}
+$endif$
+
+$if(signature)$
+\setkomavar{signature}{$signature$}
+$endif$
+
+% ==================== ENCLOSURES ====================
+$if(enclosures)$
+% Separator between "Enclosures" label and list (e.g., "Anlagen:")
+\setkomavar{enclseparator}{:}
+$endif$
+
+% ==================== CUSTOMIZATION OPTIONS ====================
+% Remove backaddress line in envelope window (uncomment to enable)
+\setkomavar{backaddress}{}
+
+% You can customize additional elements here:
+% - \setkomavar{location}{} - Text in the upper right corner
+% - \setkomavar{place}{} - Place of writing (if different from address)
+% - Font sizes, margins, spacing can be adjusted via KOMA-Script options
+
+% ==================== DOCUMENT BODY ====================
+\begin{document}
+
+\begin{letter}{%
+% Recipient address - each line from the 'to' frontmatter array
+$for(to)$
+$to$\\
+$endfor$
+}
+
+% ==================== OPENING ====================
+$if(opening)$
+\opening{$opening$}
+$else$
+% Default opening if not specified
+\opening{Sehr geehrte Damen und Herren}
+$endif$
+
+% ==================== LETTER BODY ====================
+% The main content from your markdown file is inserted here
+$body$
+
+% ==================== CLOSING ====================
+$if(closing)$
+\closing{$closing$}
+$else$
+% Default closing if not specified
+\closing{Freundliche Grüsse}
+$endif$
+
+% ==================== ENCLOSURES LIST ====================
+$if(enclosures)$
+% List of attached documents (e.g., CV, certificates)
+\encl{$for(enclosures)$$enclosures$$sep$\\$endfor$}
+$endif$
+
+\end{letter}
+
+\end{document}