feat(mobile): add PostHog analytics with autocapture and screen tracking

[saddlepaddle]

Summary

• Integrates PostHog React Native SDK for analytics in the mobile app
• Adds automatic screen tracking using expo-router's usePathname
• Enables touch autocapture for button/interaction tracking
• Sets up user identification when authenticated

Changes

• Added posthog-react-native and required Expo dependencies (expo-application, expo-device, expo-file-system, expo-localization)
• Created PostHogProvider wrapper with screen tracking and debug mode support
• Created PostHogUserIdentifier component for authenticated user identification
• Added PostHog config to lib/posthog/ with environment variable support

Test plan

• Verified events flow to PostHog dashboard (identify, screen, autocapture)
• Confirmed expo-file-system v19 works natively without AsyncStorage workaround
• Lint and typecheck pass

Summary by CodeRabbit

• New Features

  • Integrated comprehensive analytics and user session tracking capabilities throughout the mobile application

• Chores

  • Added new project dependencies including analytics library, device utilities, localization framework, and enhanced async storage management
  • Extended environment configuration with analytics-related settings and variables
  • Reorganized application initialization structure and root layout components for improved code organization

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR integrates PostHog analytics into the mobile app by adding environment configuration for PostHog credentials, creating a PostHog client and provider, refactoring the root layout to manage QueryClient and PostHog providers, and implementing components for tracking user identity and initializing analytics settings.

Changes

Cohort / File(s)	Summary
Configuration & Dependencies apps/mobile/app.config.ts, apps/mobile/lib/env.ts, apps/mobile/package.json	Added expo-localization to Expo plugins. Introduced EXPO_PUBLIC_POSTHOG_KEY and EXPO_PUBLIC_POSTHOG_HOST environment variables with URL default. Added posthog-react-native, expo-localization, and updated async-storage dependencies.
PostHog Library Setup apps/mobile/lib/posthog/client.ts, apps/mobile/lib/posthog/index.ts	Created PostHog configuration object importing env variables, defining apiKey, host, and debug/session replay options. Exported via index module for public access.
Root Layout Refactoring & Providers apps/mobile/app/_layout.tsx, apps/mobile/screens/RootLayout/RootLayout.tsx, apps/mobile/screens/RootLayout/index.ts, apps/mobile/screens/RootLayout/providers/PostHogProvider/...	Moved RootLayout implementation from app/_layout.tsx to screens directory. New RootLayout wraps app in QueryClientProvider and PostHogProvider, renders Stack with PortalHost. PostHogProvider initializes PostHog with app registration, debug mode, and screen view tracking via pathname changes.
User Identity Tracking apps/mobile/screens/RootLayout/components/PostHogUserIdentifier/PostHogUserIdentifier.tsx, apps/mobile/screens/RootLayout/components/PostHogUserIdentifier/index.ts	Introduced PostHogUserIdentifier component that subscribes to session changes, calling posthog.identify with user id and attributes when logged in, and posthog.reset on logout.

Sequence Diagrams

sequenceDiagram
    participant App as Mobile App
    participant RootLayout as RootLayout
    participant QueryProvider as QueryClientProvider
    participant PostHogProv as PostHogProvider
    participant PostHog as PostHog Instance
    participant PathTracker as PostHogInitializer

    App->>RootLayout: Mount
    RootLayout->>QueryProvider: Wrap children
    QueryProvider->>PostHogProv: Wrap children
    PostHogProv->>PostHog: Initialize with config
    PostHog-->>PostHogProv: Ready
    PathTracker->>PostHog: Register app (app_name: mobile)
    PathTracker->>PostHog: Enable debug if configured
    PathTracker->>PostHog: Capture initial screen view
    PostHogProv->>App: Render Stack + PortalHost

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sequenceDiagram
    participant Session as Session State
    participant UserIdent as PostHogUserIdentifier
    participant PostHog as PostHog Instance

    Note over Session,PostHog: User logs in
    Session->>UserIdent: Session updated with user
    UserIdent->>PostHog: identify(userId, {email, name})
    PostHog-->>UserIdent: Identified
    
    Note over Session,PostHog: User logs out
    Session->>UserIdent: Session becomes null
    UserIdent->>PostHog: reset()
    PostHog-->>UserIdent: Reset

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~22 minutes

Possibly related PRs

• feat: add PostHog event tracking across apps #476 — Adds PostHog integration with user-identification and environment configuration across desktop, web, admin, and marketing apps, mirroring the analytics setup in this mobile PR.
• feat(mobile): build out barebones mobile app #843 — Mobile app scaffold that provides the initial RootLayout structure; this PR extends it with PostHog wiring and refactors app/_layout.tsx to re-export the enhanced layout.

Poem

🐰 Hop, skip, and PostHog trace,
Identity tracked in the user's space,
Screens paint their footprints across the land,
Analytics woven with a developer's hand. ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main changes: adding PostHog analytics integration with autocapture and screen tracking to the mobile app.
Description check	✅ Passed	The PR description covers the key aspects including summary, changes made, and a detailed test plan, though it deviates from the template structure with custom formatting.

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✨ Finishing touches

• 📝 Generate docstrings

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[github-actions]

🧹 Preview Cleanup Complete

The following preview resources have been cleaned up:

• ✅ Neon database branch
• ✅ Electric Fly.io app

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