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>

scripts/run-weekly-checkins.ps1

@@ -0,0 +1,24 @@
+# Weekly coaching check-in batch (Phase 3) for Windows Task Scheduler.
+# Reads the admin API key from .env and POSTs /discovery/coaching/run, which
+# generates a check-in for every eligible user whose cadence is due.
+# Override the target with $env:IMPACTFLOW_BASE_URL (default: local container).
+
+$ErrorActionPreference = 'Stop'
+$dir     = Split-Path -Parent $PSScriptRoot          # repo root (scripts\..)
+$envFile = Join-Path $dir '.env'
+$log     = Join-Path $dir 'data\coaching-cron.log'
+$base    = if ($env:IMPACTFLOW_BASE_URL) { $env:IMPACTFLOW_BASE_URL } else { 'http://localhost:8011' }
+$ts      = (Get-Date).ToUniversalTime().ToString('yyyy-MM-ddTHH:mm:ssZ')
+
+try {
+    $line = (Select-String -Path $envFile -Pattern '^IMPACTFLOW_API_KEY=' | Select-Object -First 1).Line
+    $key  = ($line -replace '^IMPACTFLOW_API_KEY=', '').Trim()
+    if (-not $key) { throw "IMPACTFLOW_API_KEY not found in $envFile" }
+
+    $resp = Invoke-RestMethod -Method Post -Uri "$base/discovery/coaching/run" `
+        -Headers @{ 'X-API-Key' = $key } -TimeoutSec 120
+    "$ts $($resp | ConvertTo-Json -Compress)" | Add-Content -Path $log
+}
+catch {
+    "$ts ERROR: $($_.Exception.Message)" | Add-Content -Path $log
+}