[feat]: add PDF appearance customization options

- Add PDFDisplayAppearance enum with default, dark, and paper tone modes
- Implement PDFDisplaySurface view modifier for themed PDF rendering
- Add PDF appearance picker to settings with localized descriptions
- Update PDFReaderView and DualPDFReaderView to support appearance settings
- Store user preference in AppStorage with default fallback
- Bump version to 0.3.3 and build number to 23

[chore]: update project configuration and version

- Change app name from ReadPaper to Freddie
- Update objectVersion from 77 to 63
- Remove preferredProjectObjectVersion setting
- Update CURRENT_PROJECT_VERSION from 21 to 22
- Update MARKETING_VERSION from 0.3.1 to 0.3.2
- Update project.yml to match new version numbers

[feat]: add note anchoring and selection tracking

- Implement NoteAnchor model for storing selection references
- Add selection tracking to PDF and HTML readers
- Enable creating notes from selected text with anchors
- Add navigation from notes back to original selection
- Update UI with selection context and anchor indicators
- Add tests for NoteAnchor and SettingsGeneralStatus

[chore]: update project version and development team

- Increment CURRENT_PROJECT_VERSION from 19 to 20
- Update MARKETING_VERSION from 0.2.9 to 0.3.0
- Add DEVELOPMENT_TEAM setting for code signing
- Update project configuration files accordingly

[chore]: bump version to 0.2.9

- Update CURRENT_PROJECT_VERSION from 18 to 19
- Update MARKETING_VERSION from 0.2.8 to 0.2.9
- Fix BabelDoc Python executable detection to preserve symlinks
- Add babeldoc module import check during installation validation
- Update tests for new import validation behavior

[feat]: add BabelDOC installation source switching

- Support switching between official PyPI and Tsinghua TUNA mirror
- Store preference via UserDefaults to avoid SwiftData compatibility issues
- Update BabelDocToolManager to handle metadata URL and uv install parameters
- Add corresponding unit tests for installation source functionality
- Bump app version to 0.2.8

[chore]: update project configuration and BabelDOC version detection

- Update Xcode project object version and remove preferredProjectObjectVersion
- Increment CURRENT_PROJECT_VERSION to 17 and MARKETING_VERSION to 0.2.7
- Update app product name references to Freddie.app
- Improve BabelDOC version detection with simple package index fallback
- Add PythonPackageVersion struct for proper semantic version comparison
- Update tests to use simple index and fallback to metadata releases
- Add version extraction from PyPI simple index HTML

[chore]: bump version to 0.2.6

- Update MARKETING_VERSION from 0.2.5 to 0.2.6
- Increment CURRENT_PROJECT_VERSION in Xcode project and project.yml

[chore]: update marketing version to 0.2.5

[chore]: update project configuration and version

- Lower Xcode project object version from 77 to 63
- Update app name references from ReadPaper.app to Freddie.app
- Remove preferredProjectObjectVersion setting
- Increment CURRENT_PROJECT_VERSION from 14 to 15
- Update MARKETING_VERSION from 0.2.3 to 0.2.4
- Update project.yml to match new version numbers