feat: Strava Integration (OAuth, Jobs, UI)

[0jonjo]

What does this PR do?

Introduces a fully featured, robust, and lightweight integration with the Strava API to automatically sync athletes' activities into Calcpace Web, extracting vital data and estimating VO2 Max natively.

Technical Highlights 🚀

This implementation intentionally avoids bloated third-party gems, favoring a lean, native Rails approach with several architectural highlights:

• Security First: OAuth access tokens and refresh tokens are encrypted at rest using Rails 7 ActiveRecord::Encryption.
• Zero-Bloat API Client: Built a custom Strava::Client wrapping Net::HTTP to handle OAuth flow, token refreshing, and paginated data fetching without external dependencies.
• Resilient Background Sync: Implemented StravaSyncJob via ActiveJob/SolidQueue. It paginates up to 2,000 historical runs per sync, gracefully handling API rate limits, HTTP errors, and token expirations in the background.
• Database Optimization (Polylines): Instead of parsing and storing thousands of GPS trackpoints per run (which inflates DB size exponentially), the app extracts Strava's summary_polyline. This encrypted string is saved in a single text column and decoded seamlessly via JavaScript on the frontend using Leaflet, delivering high-performance maps with zero storage overhead.
• Smart Activity Importer: The Strava::ActivityImporter enforces single responsibility. It filters out non-running activities (supports Run, TrailRun, Walk), deduplicates by external_id, and maps distance/time/elevation/HR directly to the Calcpace engine for automatic VO2 Max estimation.
• Real-time Webhooks Ready: Established the foundation for Strava Webhooks (StravaWebhooksController) with challenge validation and async job triggering, ensuring the app is ready for real-time push events.

Changes

• db/migrate: Added StravaAccount table (with encrypted tokens) and map_polyline to activities.
• app/models: Added StravaAccount model and updated Activity.log.
• app/lib/strava: Created Client and ActivityImporter.
• app/jobs: Added StravaSyncJob.
• app/controllers: Added StravaAccountsController (OAuth callback) and StravaWebhooksController.
• app/views: Added Connect/Disconnect UI in accounts/show using jet_ui and implemented JS Polyline decoding in _map.html.erb.

Testing

• 100% Test Coverage: All scenarios tested using WebMock to simulate Strava API responses, token expirations, and webhook challenge validations.

How to test manually

1. Start the server: bin/dev
2. Navigate to Settings > Account.
3. Click Connect with Strava and authorize the application.
4. Observe the background job syncing activities.
5. View an imported activity to see the generated metrics and the rendered Leaflet map.

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