Add biweekly pay schedule with projected paychecks and dashboard integration

- Add PaySchedule model (anchorDate + amountCents + active flag)
- Add /pay-schedule API route (GET, POST, DELETE)
- Project biweekly pay dates from anchor; deduplicate against manual paychecks
- Merge projected paychecks into dashboard totals and daily chart
- Fix DST day-shift bug in getProjectedPayDates by using Date.UTC throughout
- Rewrite paycheck workspace: schedule panel at top, manual entry below,
  projected dates with "Mark received" buttons, confirmed badges
- Pass paySchedule context to Ollama insight prompt

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

prisma/migrations/20260323161758_add_monthly_insight_unique/migration.sql

@@ -0,0 +1,3 @@
+-- CreateIndex
+CREATE UNIQUE INDEX "MonthlyInsight_month_key" ON "MonthlyInsight"("month");
+