Add Jinja2 web UI with Bootstrap 5 dark theme

- app/templates/: base layout with sidebar nav + 6 pages
  (dashboard, printers, jobs, filaments, todos, pricing)
- app/routers/ui.py: HTML routes querying the DB live
- API routes moved to /api/* prefix
- requirements: jinja2, python-multipart

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

app/main.py

@@ -5,6 +5,7 @@ from fastapi import FastAPI
 
 from app.db import check_db, run_migrations
 from app.routers import filaments, pricing, print_jobs, printers, todos
+from app.routers import ui
 
 logger = logging.getLogger("pops")
 
@@ -22,16 +23,15 @@ async def lifespan(app: FastAPI):
 
 app = FastAPI(title="POPS", lifespan=lifespan)
 
-app.include_router(printers.router)
-app.include_router(filaments.router)
-app.include_router(print_jobs.router)
-app.include_router(todos.router)
-app.include_router(pricing.router)
+# JSON API
+app.include_router(printers.router, prefix="/api")
+app.include_router(filaments.router, prefix="/api")
+app.include_router(print_jobs.router, prefix="/api")
+app.include_router(todos.router, prefix="/api")
+app.include_router(pricing.router, prefix="/api")
 
-
-@app.get("/")
-def root():
-    return {"message": "Hello from POPS"}
+# Web UI (must come after API to avoid route shadowing)
+app.include_router(ui.router)
 
 
 @app.get("/health")