Add Windows Task Scheduler runner for weekly check-ins

scripts/run-weekly-checkins.ps1: pure-Windows equivalent of the cron script —
reads the admin API key from .env and POSTs /discovery/coaching/run via
Invoke-RestMethod, logging to data/coaching-cron.log. README documents the
Register-ScheduledTask command (weekly, StartWhenAvailable + WakeToRun) for a
more robust schedule than WSL cron.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -886,6 +886,24 @@ Running weekly services all cadences — the endpoint skips users who are not ye
 due (biweekly/monthly), so a weekly tick is the finest needed. Output is
 appended to `data/coaching-cron.log`. (On WSL, cron only runs while WSL is up.)
 
+**More robust: Windows Task Scheduler.** `scripts/run-weekly-checkins.ps1` does
+the same POST from Windows (reading the key from `.env`, hitting
+`localhost:8011`). Register it to run weekly — and to catch up if the machine
+was asleep — from PowerShell:
+
+```powershell
+$action  = New-ScheduledTaskAction -Execute 'powershell.exe' `
+  -Argument '-NoProfile -ExecutionPolicy Bypass -File "C:\syncdata\impactflow-discovery\scripts\run-weekly-checkins.ps1"'
+$trigger = New-ScheduledTaskTrigger -Weekly -DaysOfWeek Monday -At 8am
+$settings = New-ScheduledTaskSettingsSet -StartWhenAvailable -WakeToRun
+Register-ScheduledTask -TaskName 'ImpactFlow Weekly Check-ins' `
+  -Action $action -Trigger $trigger -Settings $settings `
+  -Description 'Phase 3 weekly coaching check-in batch'
+```
+
+Use either the WSL cron or the Task Scheduler job — not both is fine, but
+running both is harmless since the endpoint dedupes by due-ness.
+
 ## Quick Start With Docker
 
 This path requires Docker Desktop or another Docker Engine installation with