feat(insight-cards): add real-time agent-generated insight cards for …

[Mainnet-ops]

…dashboard

Add backend service that aggregates payroll, workforce, liquidity, and schedule data into severity-ranked insight cards. Expose via GET /api/v1/insight-cards with configurable lookback window.

Frontend InsightCards component renders cards on the Home page with severity badges, metrics, and deep-link actions. 16 unit tests cover all card generation paths including edge cases and partial failures.

Closes #1299
Closes #1305
Closes #1296
Closes #1295
Backend (3 new files + 1 modified)

• backend/src/schemas/insightCardsSchema.ts — Zod schema defining InsightCard (id, title, body, category, severity, metric, actionRoute) and InsightCardsResponse
• backend/src/services/insightCardsService.ts — Core service that runs 4 builders in parallel (payroll, workforce, liquidity, schedule), merges results, and sorts by severity. Each builder is wrapped in Promise.allSettled so partial failures don't break the whole response
• backend/src/routes/insightCardsRoutes.ts — GET /api/v1/insight-cards?windowDays=30 with JWT auth + org isolation + EMPLOYER role gate
• backend/src/app.ts — Route registered

Frontend (3 new files + 1 modified)

• frontend/src/services/insightCardsApi.ts — Typed axios client
• frontend/src/components/InsightCards.tsx — Renders a responsive grid of cards with severity badges, metric callouts, category icons, loading skeletons, and error/retry states
• frontend/src/pages/Home.tsx — InsightCards section inserted between the hero CTA and the static feature cards

Tests (16 passing)

• backend/src/services/__tests__/insightCardsService.test.ts — Covers all card IDs: payroll disbursed/failure/no-activity, workforce headcount/high-inactive/no-employees, liquidity not-configured/zero-balance/balance, schedule summary/none/upcoming, plus severity ordering, response shape, and partial-failure resilience