feat(send): improve Lightning send failure recovery

[pwltr]

Description

Ports the iOS Lightning send-failure retry behavior to Android.

• Shows the send failure screen for failed Lightning sends instead of relying only on toasts.
• Maps LDK payment failure reasons to localized, user-facing strings.
• Uses send-specific copy for route-not-found and retries-exhausted failures.
• Keeps generic payment failure copy reusable outside the send flow.
• Shows the correct failure title for Lightning vs on-chain send errors.
• Always shows Retry on the Lightning send failure screen.
• Retry clears local/VSS network graph data and scorer/pathfinding score data before restarting ldk-node.
• Retry waits for local routing data to be usable again without requiring a newer remote RGS snapshot timestamp.
• Guards retry state in WalletViewModel so overlapping retry flows cannot surface stale timeout errors.
• Resets send navigation back to the retry route instead of stacking retry screens on top of the failure screen.

Closes #829

Preview

Screen.Recording.2026-08-06.at.16.16.23.mov

QA Notes

Tested on mainnet emulator:

• Confirmed ROUTE_NOT_FOUND surfaces user-facing send copy.
• Confirmed retry deletes local graph, VSS graph, scorer, and external scores cache.
• Confirmed retry restarts from an empty graph and accepts the same RGS snapshot timestamp.
• Confirmed retry waits through RGS/scorer refresh and returns to the send confirmation path.
• Confirmed no stale retry timeout after repeated retry attempts.

Automated checks:

• compileDevDebugKotlin
• PaymentFailureReasonExtTest.kt
• AppViewModelSendFlowTest.kt
• TransferViewModelTest.kt
• detekt