feat: bootstrap MediaStationGo (Go + React rewrite of MediaStation)

Adopt the cropflre/nowen-video tech stack and rebuild the project from
scratch:

  - Backend: Go 1.25 + Gin + GORM + SQLite (WAL) + JWT + WebSocket hub.
    Layered packages config / database / model / repository / service /
    middleware / handler. Default admin (admin/admin123) seeded on first
    run; /api routes for auth, libraries, media, stream and admin
    panels. WebSocket scan-progress events at /api/ws.
  - Frontend: React 18 + Vite 5 + Tailwind 3.4 + Zustand + axios +
    react-router 6 + lucide-react + framer-motion + hls.js. Pages for
    Login / Home / Library / Search / MediaDetail / Player / Admin
    (Library, Users, Settings tabs).
  - Distribution: multi-arch Dockerfile (frontend -> backend -> Alpine
    runtime), docker-compose.yml, GitHub Actions for CI and GHCR
    publish, Makefile, env-prefixed config (MEDIASTATION_*).
  - Docs: README, CONTRIBUTING, .env.example, config.example.yaml.

Backend builds, vets and tests pass. Frontend builds via tsc -b && vite
build (250 kB JS / 16 kB CSS, gzipped 84 / 4 kB).

CONTRIBUTING.md

@@ -0,0 +1,41 @@
+# Contributing to MediaStationGo
+
+Thanks for taking the time to contribute! This document is intentionally short —
+prefer asking in an issue/PR over re-reading rules.
+
+## Local development
+
+```bash
+# Backend (Go 1.25+ required)
+make dev               # MEDIASTATION_APP_DEBUG=true go run ./cmd/server
+
+# Frontend (Node 20+ required)
+make dev-web           # vite dev server on :3000, proxies /api -> :8080
+```
+
+Default admin: `admin / admin123` — change it after first login.
+
+## Code style
+
+- **Go**: keep packages small, services thin, errors wrapped with `%w`. Run
+  `go vet ./...` and `go test ./...` before pushing.
+- **TypeScript**: `strict: true` is on. Prefer `interface` over `type` for
+  object shapes. Components live next to their page when not reused.
+- Comments should explain *why*, not *what*. Avoid emoji in code.
+
+## Commit / PR conventions
+
+- Conventional commits encouraged: `feat:`, `fix:`, `docs:`, `refactor:`, `chore:`.
+- One concern per PR. Update the README/docs when behaviour changes.
+- CI must pass: `go vet`, `go test`, frontend `tsc -b && vite build`.
+
+## Issue triage
+
+When filing a bug please include:
+
+1. The steps to reproduce.
+2. The expected and actual behaviour.
+3. Logs from `docker logs mediastation-go` (or stdout if running locally).
+4. Your deployment context (NAS model, OS, Docker version).
+
+Thanks for keeping the project healthy!