fix(mobile): restore chat height after keyboard dismiss

[cha1latte]

Summary

• use react-native-keyboard-controller padding behavior in both Android chat screens
• keep the existing animated keyboard-opening path and vertical offset
• add a regression contract that rejects the stale height behavior

Root cause

The controller's height behavior writes animated { height, flex: 0 } while the keyboard is open, then returns {} when closed. Reanimated can retain those native properties and leave the chat wrapper keyboard-shortened after dismissal.

An explicit undefined reset was also rejected by real Pixel testing because it cleared the wrapper's static flex: 1. Padding behavior avoids both failure modes: it never writes height/flex and closes to an explicit numeric paddingBottom: 0.

Verification

• reproduced on Pixel 9a with a 965 px lower dead area
• device-tested and rejected the first reset attempt before this correction
• official-main Expo suite: 15 passed
• focused regression: 3 passed
• Expo TypeScript and scoped Biome checks
• git diff --check
• independent review: no Critical or Important findings
• installed the corrected preview APK in place on a Pixel 9a and exercised the full closed -> open -> dismissed keyboard cycle
• before/dismissed screenshots were byte-identical, and the composer returned from [34,1218][1046,1340] open to [34,2120][1046,2242] dismissed

The aggregate PR diff is three focused files: both chat screens and the regression test.