feat: add stock database with prisma for portfolio persistence

- Initialize Prisma with SQLite and Stock model
- Create database service layer with singleton client
- Add API routes for stock CRUD operations
- Integrate database with analyze page to persist ticker entries
- Add Playwright tests for stock database functionality

docs/superpowers/specs/2026-05-14-prisma-stock-model.md

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+# Prisma Stock Model Implementation Spec
+
+## Goal
+Initialize Prisma ORM with SQLite database and create a Stock model to persist manually added stock tickers in the AITrader analyze route.
+
+## Architecture
+- **ORM**: Prisma with SQLite datasource
+- **Database file**: `prisma/dev.db`
+- **Model**: `Stock` with id, ticker, optional notes, and timestamps
+- **Integration**: API routes for CRUD operations, integrated with analyze.tsx
+
+## Design Decisions
+
+### Stock Model Schema
+```prisma
+model Stock {
+  id        String   @id @default(cuid())
+  ticker    String   @unique
+  notes     String?
+  createdAt DateTime @default(now())
+  updatedAt DateTime @updatedAt
+}
+```
+
+**Rationale for `notes` field**: Included for future extensibility (user notes on watched stocks). Nullable to avoid breaking changes.
+
+### Implementation Approach
+- Single migration (`init`) for all model fields
+- SQLite for development simplicity (matches plan)
+- Prisma client singleton pattern for React Router 7 compatibility
+
+## Files to Create/Modify
+
+### Task 1: Initialize Prisma
+- `prisma/schema.prisma` - Prisma schema with Stock model
+- `prisma/dev.db` - SQLite database (generated)
+- `prisma/migrations/..._init/migration.sql` - Initial migration (generated)
+
+## Success Criteria
+1. `prisma/schema.prisma` exists with valid Stock model
+2. `npx prisma generate` completes without errors
+3. `npx prisma migrate dev --name init` creates `prisma/dev.db`
+4. Git commit created with prisma/ changes
+
+## Dependencies to Install
+- `prisma` (dev dependency)
+- `@prisma/client` (runtime dependency)