Add CSV export functionality for setlists

[johnrobertdelinila]

Summary

Implements CSV export functionality allowing musicians to export setlists
for sharing with band members and venue coordinators.

Changes Made

Core Layer

• Added ISetlistExportService interface

Infrastructure Layer

• Implemented SetlistExportService with CSV generation
• Proper CSV escaping for special characters (commas, quotes, newlines)
• Registered service in dependency injection

Web Layer

• Created SetlistExportController with /api/SetlistExport/{id}/csv
  endpoint
• Added "Export" button to Setlists.razor page
• Authorization checks (users can only export their own setlists)

Features

Setlist Metadata:

• Name, description, venue, performance date, duration, song count, export
  timestamp

Song Details:

• Position, title, artist, key, BPM, duration, genre, difficulty
• Performance notes, transition notes, encore/optional flags
• Custom BPM/key overrides

Technical Implementation:

• Follows Clean Architecture pattern
• Comprehensive error handling and logging
• Secure authorization checks
• Sanitized CSV output

Testing

43 comprehensive unit tests:

• 26 tests for SetlistExportService
• 17 tests for SetlistExportController

Coverage includes:

• Authorization (users can't export others' setlists)
• CSV formatting and escaping
• Edge cases (empty setlists, special characters)
• Error handling

Run tests:

dotnet test --filter "FullyQualifiedName~SetlistExport"

Musician Use Case

Musicians can now:
1. Navigate to their setlists page
2. Click "Export" on any setlist
3. Download a CSV file with all song details
4. Share with band members or venue staff
5. Import into Excel/Google Sheets

Checklist

-  Code follows project conventions
-  Comprehensive test coverage (80%+)
-  No breaking changes
-  Clean Architecture maintained
-  Authorization implemented
-  Error handling included
-  Production-ready code