Feature: Automated weekly contribution refresh and score recalculation

[sajeetharan]

Problem

Developer profiles, scores, and ranks become stale unless the full ingestion pipeline is run manually. Stale identity cards and rankings weaken trust and remove the main reason for developers to return.

Proposed solution

Add a scheduled, incremental refresh that updates contribution metrics from supported sources, recalculates scores and ranks, and records enough history to explain changes.

Acceptance criteria

• Refresh claimed and recently viewed profiles on a weekly schedule
• Fetch GitHub and linked Stack Overflow metrics incrementally with bounded concurrency
• Recalculate scores with the shared scoring implementation
• Recalculate affected global, country, city, and language ranks consistently
• Record refresh status, source freshness, failures, and retry eligibility
• Preserve the last valid metrics when one upstream source is unavailable
• Respect API quotas, backoff instructions, and a configurable RU/cost budget
• Make the job idempotent and safe to resume after interruption
• Publish refresh diagnostics without exposing credentials or private profile data
• Add tests for partial-source failure, retries, and unchanged profiles

Retention outcome

Create a reliable contribution → refresh → rank movement → return loop.

Related issues

• Impact history and rank movement: Feature: Developer impact history and rank movement dashboard #111
• Weekly ranking digest: Weekly ranking digest email #22
• Analytics and return visits: Analytics: Measure engaged sessions and post-card retention #121