Add native Swift iOS app for RSVP speed reading

[Copilot]

Description

Adds a native Swift + SwiftUI iOS app (ios/) delivering the same RSVP speed reading experience as the existing TUI and web frontends — no third-party dependencies.

App structure (ios/)

• Cheetah.xcodeproj/ — Xcode project targeting iOS 16+, Swift 5.9, linked against libz.tbd and PDFKit.framework
• Models/ — ReadingEngine (@MainActor ObservableObject, Timer-driven word advancement), Document (SHA-256 hashing via CryptoKit for session identity), Settings (UserDefaults-backed), SessionStore (JSON-serialised singleton)
• Parsers/DocumentParser — handles TXT/MD (plain String), PDF (PDFKit), and ZIP-based formats (DOCX, EPUB, ODT) via a pure-Swift ZIP reader with raw-deflate decompression through a zlib bridging header; uses XMLParser (SAX, iOS-compatible — XMLDocument is macOS-only)
• Views/ — HomeView (file picker via fileImporter, recent sessions), ReadingView (full-screen RSVP, drag-to-seek scrubber, speed panel, go-to %, paragraph nav), SettingsView
• CheetahTests/ — 30+ unit tests covering Document model, ReadingEngine navigation/speed/state, Settings presets, and SessionStore CRUD

Feature parity with web/TUI

Feature	Detail
Speed control	50–2000 WPM slider + ±50 WPM; presets 1–9 = 200–1000 WPM
Punctuation delay	Sentence ×1.3, clause ×1.15 — matches Go backend
Context words	Configurable previous + up to 5 next words
Progress scrubber	Drag-to-seek + go-to-% sheet
Auto-save / resume	Position saved every N words, matched by SHA-256 hash

Additional Context

Build and test:

# Open in Xcode
open ios/Cheetah.xcodeproj

# CLI build
xcodebuild -project ios/Cheetah.xcodeproj -scheme Cheetah \
  -destination 'platform=iOS Simulator,name=iPhone 15' build

# CLI test
xcodebuild -project ios/Cheetah.xcodeproj -scheme CheetahTests \
  -destination 'platform=iOS Simulator,name=iPhone 15' test

.gitignore updated to exclude Xcode user data and derived build artefacts. README.md and SPECIFICATION.md updated to document iOS as a supported platform.

Type of change

• 🐛 Bug fix
• ✨ New feature
• 💥 Breaking change
• 📚 Documentation update
• 🎨 Code style or formatting
• ⚡ Performance
• 🧪 Test coverage
• 📦 Packaging
• 👷 CI improvement

Checklist

• I have performed a self-review of my code
• I have tested my changes and confirmed there are no regressions

Original prompt

Add a new native swift experience of timlinux/cheetah for iOS users. It must provide the same features and experience as the web and tui apps

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