[377][378][379][380] [BE-029–BE-032] Auto-sweep worker, yield calculator, toggle API, and report notifications

[josephchimebuka]

Closes #377
Closes #378
Closes #379
Closes #380

Summary

Implements backend issues #377, #378, #379, and #380:

Issue	Ticket	Deliverable
#377	BE-029	Auto-sweep scheduler background worker (sweep_worker.rs)
#378	BE-030	POST /api/yield/toggle-auto preference endpoint
#379	BE-031	Off-chain real-time yield calculator (yield_calc.rs)
#380	BE-032	Daily/weekly yield report notification scheduler (notifications.rs)

#377 — Auto-sweep scheduler

• Polls users with auto_earn_enabled = true
• Sweeps idle available_balance into earning_balance and logs DEPOSIT transactions
• Configurable via SWEEP_POLL_INTERVAL_SECS and SWEEP_MIN_IDLE_AMOUNT

#378 — Toggle auto-earn API

• POST /api/yield/toggle-auto saves users.auto_earn_enabled
• Returns confirmation payload with current auto_earn_enabled state
• GET /api/yield/balance also exposes auto_earn_enabled

#379 — Off-chain yield calculator

• Linear interest estimate since last_yield_sync_at using current APY
• Balance API returns accrued_interest and total_earning_balance
• format_yield_feed_fields helper exposed for feed query responses

#380 — Yield report notifications

• Daily and weekly schedulers for users with positive earning balances
• Sends Expo push notifications when earned yield exceeds YIELD_REPORT_THRESHOLD
• Uses user_push_tokens table and Expo Push API

Database migration

20260627000000_yield_auto_earn_and_notifications.sql adds:

• users.auto_earn_enabled, last_daily_yield_report_at, last_weekly_yield_report_at
• user_yield_balances.last_yield_sync_at
• user_push_tokens table

Test plan

• cargo build succeeds
• Unit tests for yield_calc and notification period math pass
• Run migration and verify POST /api/yield/toggle-auto toggles auto_earn_enabled
• Confirm GET /api/yield/balance returns live accrued_interest / total_earning_balance
• Seed auto-earn user with idle balance; verify sweep worker moves funds
• Register Expo push token; verify scheduler sends notification above threshold

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[ONEONUORA]

Great job @josephchimebuka
Thank you for your contribution