feat: refactor to FastAPI architecture v2.0

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/main.py

@@ -0,0 +1,26 @@
+"""FastAPI application entry point."""
+
+from fastapi import FastAPI
+from fastapi.staticfiles import StaticFiles
+from fastapi.responses import FileResponse
+import os
+
+from app.api.router import api_router
+from app.config import VERSION
+
+app = FastAPI(
+    title="Scenar Creator",
+    description="Web tool for creating timetable scenarios from Excel or inline forms",
+    version=VERSION,
+)
+
+app.include_router(api_router)
+
+# Static files
+static_dir = os.path.join(os.path.dirname(__file__), "static")
+app.mount("/static", StaticFiles(directory=static_dir), name="static")
+
+
+@app.get("/", include_in_schema=False)
+async def root():
+    return FileResponse(os.path.join(static_dir, "index.html"))