feat: implementar 12 mejoras, tests, docs y optimizaciones

- Fase A: license templates, search history, cost estimator
- Fase B: import URL, bulk ZIP, batch download
- Fase C: comparison mode, mesh validation, measurement tool
- Fase D: cross-section clipping, overhang heatmap, layer animation
- Refactor Pydantic/SQLAlchemy warnings
- 24 tests pytest
- README actualizado
- WebP thumbnails, lazy loading, cache headers

app/main.py

@@ -0,0 +1,38 @@
+from fastapi import FastAPI
+from fastapi.staticfiles import StaticFiles
+from fastapi.responses import FileResponse
+from app.database import engine, Base
+from app.routers import models
+from app.migrate import run_migrations
+import os
+
+# Create tables and run migrations
+Base.metadata.create_all(bind=engine)
+run_migrations()
+
+app = FastAPI(title="STL Repository", version="2.1.0")
+
+app.include_router(models.router)
+
+# Serve static files
+app.mount("/static", StaticFiles(directory="static"), name="static")
+
+# Serve uploads, thumbnails and images directly
+app.mount("/uploads", StaticFiles(directory="uploads"), name="uploads")
+app.mount("/thumbnails", StaticFiles(directory="thumbnails"), name="thumbnails")
+app.mount("/images", StaticFiles(directory="images"), name="images")
+
+
+@app.get("/")
+def root():
+    return FileResponse("static/index.html")
+
+
+@app.get("/upload")
+def upload_page():
+    return FileResponse("static/upload.html")
+
+
+@app.get("/model/{model_id}")
+def detail_page(model_id: int):
+    return FileResponse("static/detail.html")