Replace Next.js application with React/Vite frontend and Go API

[wechuli]

Implement the complete migration described in
wealthboard-go-vite-migration-brief.md.

This is an implementation task, not a planning or scaffolding task. Complete the
migration in one pull request and leave the repository in a runnable state. You can perform multiple implementation passes on the same PR and generate a representative fictional database.

Requirements:

• Replace the Next.js runtime with a client-side React/Vite application.
• Implement the backend in Go using Chi, sqlc, Goose, and SQLite.
• Preserve all current user-facing behavior and financial/domain invariants.
• Preserve existing user data and provide a tested migration path.
• Implement browser authentication and scoped API keys as specified.
• Keep strict owner scoping on every user-owned resource.
• Preserve integer minor-unit monetary storage and transactional behavior.
• Remove Next.js and its server-side runtime from the final deployment.
• Update Docker, Kubernetes, local-development, backup, and deployment configuration.
• Do not stop after creating skeleton packages, sample endpoints, or placeholder handlers.
• Do not leave TODO implementations for required functionality.
• Do not silently omit features that are difficult to migrate.

Before finishing:

1. Run Go unit and integration tests.
2. Run frontend type checking and tests.
3. Run the complete end-to-end test suite.
4. Test migration against a copy of the existing SQLite database.
5. Build the production frontend and backend images.
6. Confirm that the production deployment no longer starts Next.js.
7. Document any unavoidable deviation from the migration specification in the PR.

Use incremental commits so work is recoverable, but deliver one cohesive pull request.
If a requirement is unclear, inspect the existing implementation and preserve its
observable behavior.