Scaffold backend (FastAPI/uv) and frontend (SvelteKit/bun)

Backend: FastAPI app with health check, AppError hierarchy, stderr
logging via LOG_LEVEL, ruff+pyright(strict) config, pytest passing.

Frontend: SvelteKit (TS) with prettier, eslint, vitest (unit +
component), adapter-node for self-hosted deployment on Zeus.

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

backend/app/main.py

@@ -0,0 +1,33 @@
+"""Sagaphone FastAPI entrypoint.
+
+Routes are added as features land (see ../SPEC.md and ../spec/*.md).
+This currently only wires up app creation, logging, and a health check
+so the scaffold is runnable end to end.
+"""
+
+from __future__ import annotations
+
+import logging
+
+from fastapi import FastAPI, Request
+from fastapi.responses import JSONResponse
+
+from app.errors import AppError
+from app.logging_config import configure_logging
+
+configure_logging()
+logger = logging.getLogger(__name__)
+
+app = FastAPI(title="Sagaphone", version="0.1.0")
+
+
+@app.exception_handler(AppError)
+async def app_error_handler(_request: Request, exc: AppError) -> JSONResponse:
+    """Edge-catch: translate AppError subclasses into clean HTTP responses."""
+    logger.error("request failed: %s", exc.message)
+    return JSONResponse(status_code=exc.status_code, content={"error": exc.message})
+
+
+@app.get("/health")
+async def health() -> dict[str, str]:
+    return {"status": "ok"}