chore(mobile): align all 7 Expo apps to SDK 55

Upgraded 6 apps from SDK 52/54 to SDK 55 (matrix was already on 55).
All apps now consistently use:
- Expo SDK ~55.0.5
- React Native 0.83.2
- React 19.2.0
- expo-router ~55.0.5
- NativeWind ~4.2.3

Before: 3 different SDK versions (52, 54, 55)
After:  1 version (55) across all 7 mobile apps

Added docs/EXPO_SDK_UPGRADE.md with testing checklist.

Note: pnpm install + device testing required to validate the upgrades.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/EXPO_SDK_UPGRADE.md

@@ -0,0 +1,85 @@
+# Expo SDK Upgrade Guide
+
+**Current State (2026-03-28):**
+
+| App | Expo SDK | React Native | Router | Status |
+|-----|----------|-------------|--------|--------|
+| matrix | **55** | 0.83.2 | ~55.0.5 | Target version |
+| manacore | 54 | 0.81.5 | ~6.0.15 | Needs upgrade |
+| manadeck | 54 | 0.81.4 | ~6.0.10 | Needs upgrade |
+| picture | 54 | 0.81.4 | ~6.0.10 | Needs upgrade |
+| traces | 54 | 0.81.4 | ~6.0.0 | Needs upgrade |
+| chat | **52** | 0.76.7 | ~4.0.6 | Needs upgrade (2 majors!) |
+| context | **52** | 0.76.9 | ~4.0.6 | Needs upgrade (2 majors!) |
+
+**Target:** All apps on Expo SDK 55
+
+## Breaking Changes SDK 52 → 55
+
+### expo-router
+- v4 (SDK 52) → v55 (SDK 55): Major API change
+- Router is now versioned with the SDK (no more separate major versions)
+- `expo-router/entry` still works as main entry point
+
+### React
+- React 18.3 → React 19.2
+- New `use()` hook, improved Suspense
+
+### React Native
+- 0.76 → 0.83: New Architecture enabled by default
+- Fabric renderer is default
+- Bridgeless mode
+
+### NativeWind
+- v3/v4 → v4.2.3: Should be compatible if already on v4
+
+## Upgrade Steps (Per App)
+
+```bash
+# 1. Use Expo upgrade tool
+cd apps/{app}/apps/mobile
+npx expo install expo@~55.0.5 --fix
+
+# 2. This auto-upgrades compatible dependencies
+# For manual deps, use:
+npx expo install react-native@0.83.2 react@19.2.0 expo-router@~55.0.5
+
+# 3. Update NativeWind
+npx expo install nativewind@~4.2.3
+
+# 4. Fix breaking changes
+# - Check for deprecated APIs
+# - Test navigation (expo-router changes)
+# - Test NativeWind styles
+
+# 5. Clear caches and test
+npx expo start -c
+```
+
+## Recommended Upgrade Order
+
+1. **traces** (simplest app, minimal deps)
+2. **manadeck** (medium complexity)
+3. **picture** (has image handling)
+4. **manacore** (hub app, important)
+5. **context** (SDK 52 → 55, bigger jump)
+6. **chat** (SDK 52 → 55, most complex mobile app)
+
+## Shared Dependencies to Update
+
+All mobile apps share these workspace packages:
+- `@manacore/shared-ui` (React Native components)
+- `@manacore/shared-theme` (theme system)
+- `@manacore/shared-auth` (auth service)
+
+These should be tested with React 19 / RN 0.83 before upgrading apps.
+
+## Testing Checklist (Per App)
+
+- [ ] App starts without errors (`npx expo start`)
+- [ ] Navigation works (all routes)
+- [ ] Auth flow (login, logout, token refresh)
+- [ ] NativeWind styles render correctly
+- [ ] App-specific features work
+- [ ] iOS simulator test
+- [ ] Android emulator test (if applicable)