Add DateText validation and Receipt Scanning docs for Smart Label Capture

[raffaelefarinaro]

Summary

• Document the new DateText field type across the validation flow partials and per-SDK Smart Label Capture advanced pages
• Add Receipt Scanning (Beta) documentation partial covering the LabelCaptureAdaptiveRecognitionOverlay/Listener integration and ReceiptScanningResult schema
• Add receipt scanning gif asset and surface it on the SLC intro page
• Update features.json with the new capabilities

Test plan

• Build the docs site locally and verify the SLC intro page renders the new receipt scanning gif
• Verify the DateText sections render correctly across all SDK platforms (Android, iOS, Web, React Native, Flutter, Capacitor, Cordova, .NET Android/iOS)
• Verify the Receipt Scanning beta partial appears where expected and the result table renders cleanly

🤖 Generated with Claude Code

[lucatorella]

this is huge, I'm sure we can compress it by a lot