Mobile signing

[nanaabdul1172]

closes #249

Summary
I've successfully implemented a signing confirmation screen for PocketPay Mobile that separates the user's approval to sign from the actual transaction execution.

✅ Core Implementation

1. New Screen Component (
   sign-confirmation.tsx
   )

Full-screen signing confirmation interface
Transaction summary with all payment details
Security information explaining signing implications
Warning banner about irreversibility
Privacy notice about hidden technical details
Cancel and Sign Transaction buttons
Complete error handling and validation
Theme-aware styling (light/dark mode)
Full accessibility support
2. Updated Navigation (
send.tsx
)

Modified payment flow to include sign-confirmation step
New flow: Send → Sign Confirmation → Review Transaction → Payment Success
📚 Comprehensive Documentation (6 Files)
IMPLEMENTATION_SUMMARY.md

• Technical overview and architecture
  signing-confirmation-flow.md
• Detailed flow design and patterns
  sign-confirmation-test-plan.md
• 12 test categories, comprehensive test scenarios
  SIGNING_CONFIRMATION.md
• Multi-audience guide (developers, users, QA, security, designers, DevOps)
  SIGNING_CONFIRMATION_COMPLETE.md - Implementation completion summary
  SIGNING_CONFIRMATION_CHECKLIST.md - Verification checklist with 100+ items
  Plus updates to:

navigation-map.md

• Added new route
  README.md
• Updated with sign-confirmation info
  🧪 Tests (
  sign-confirmation.test.tsx
  )
  Comprehensive unit tests covering all functionality
  Contact resolution, validation, navigation, cancellation
  Edge cases, accessibility, theme integration
  ~50 test cases across 12 test suites
  ✨ Key Features
  Security:

Private key never accessed by this screen
Sensitive internals (XDR, sequence numbers) hidden
Safe cancellation with confirmation
Clear user consent mechanism
UX:

Clear separation: approval vs execution
Educational security information
Contact name resolution
Address truncation for readability
Improved error prevention
Technical:

No breaking changes to existing code
Compatible with signer handoff architecture
Future-proof for external wallet integration
Theme-aware, accessible, platform-optimized
📋 All Acceptance Criteria Met
✅ Signing confirmation screen is added
✅ Transaction details are shown
✅ Users can cancel
✅ Sensitive internals are hidden
✅ The flow fits current navigation

[El-swaggerito]

This PR cannot be merged automatically because it has merge conflicts.

Please update the branch with the latest base branch and resolve the conflicts.

After the conflicts are resolved and checks pass, the automation can review it again.