Complete the full-stack international Chinese platform

[computersciencefreshmen]

What changed

• Consolidated the project into a self-contained Vue 3, Fastify 5, and SQLite platform in the canonical repository.
• Completed student, teacher, and administrator workflows for courses, appointments, classrooms, assignments, notifications, files, dialogue, and teacher verification.
• Hardened authentication, authorization, runtime configuration, uploads, real-time tickets, rate limits, SMTP, and external AI boundaries.
• Added production container operations, 53 API tests, four cross-role browser E2E workflows, and CI validation.
• Rebuilt the Chinese and English README files as complete product, architecture, setup, security, verification, and scope documentation.

Why

The earlier repositories and historical backend state made project completeness ambiguous. This PR establishes computersciencefreshmen/International_Chinese_Platform as the single canonical, runnable source of truth.

Impact

• New teachers require explicit administrator verification before public discovery, course publishing, or new appointment acceptance.
• Production configuration now fails closed for insecure or malformed settings.
• Uploads stream to disk with type checks, quotas, concurrency limits, atomic finalization, and cleanup.
• Existing deployment boundaries are documented honestly: SQLite is single-instance, SMTP/TURN are conditional integrations, and external certificate/OCR validation is not included.

Validation

• pnpm check — formatting, ESLint, 53/53 API tests, production build
• Production Playwright E2E — all four cross-role workflows passed against a fresh database
• pnpm audit --prod --registry=https://registry.npmjs.org — no known vulnerabilities
• docker compose config --quiet — valid
• Final security review — no remaining P0/P1 findings