ProPresenter .probundle files are ZIP archives containing a single .pro
presentation with embedded media assets. This adds read/write support
verified against actual ProPresenter 7 exports.
- PresentationBundle: wrapper class (Song + media files + .pro filename)
- ProBundleReader: reads .probundle ZIPs, applies Zip64Fixer for PP exports
- ProBundleWriter: writes standard ZIP with media-first entry order
- ProFileGenerator: media URLs now include URL.local with LocalRelativePath
- 9 tests covering error handling, round-trip, PP export compat, ZIP format
- ref/TestBild.probundle: verified importable by ProPresenter 7
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