Restructure into backend/ and frontend/ subprojects

- backend/ uses proper Python src layout (src/media_library_viewer_api/)
  with pyproject.toml, hatchling build, and PYTHONPATH=src convention
- frontend/ is a Vite + React + TypeScript SPA
- archive/ preserves the original Streamlit prototype for reference
- Cleaned up root to only contain docs, license, and subproject dirs
- Updated README for the new dual-subproject architecture

backend/src/media_library_viewer_api/main.py

@@ -0,0 +1,51 @@
+"""FastAPI application entrypoint."""
+
+from __future__ import annotations
+
+from contextlib import asynccontextmanager
+
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+
+from media_library_viewer_api.routers import dashboard, monitoring, media, files, jobs
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    """Application lifespan — startup/shutdown."""
+    yield
+
+
+app = FastAPI(
+    title="Media Library Viewer API",
+    version="0.1.0",
+    description="Backend API for Jellyfin media browsing, SSH file inspection, and server monitoring.",
+    lifespan=lifespan,
+)
+
+# CORS for development (Vite runs on :5173)
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=[
+        "http://localhost:5173",
+        "http://localhost:3000",
+        "http://127.0.0.1:5173",
+        "http://127.0.0.1:3000",
+    ],
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+# Register routers
+app.include_router(dashboard.router)
+app.include_router(monitoring.router)
+app.include_router(media.router)
+app.include_router(files.router)
+app.include_router(jobs.router)
+
+
+@app.get("/api/health")
+def health_check() -> dict[str, str]:
+    """Simple health check endpoint."""
+    return {"status": "ok"}