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/logging_config.py

@@ -0,0 +1,25 @@
+"""Logging setup for the backend.
+
+Follows the project's output contract: all log output goes to stderr,
+level controlled via the LOG_LEVEL env var (default INFO). This is server
+logging, not the request/response payload — that stays in FastAPI's
+responses.
+"""
+
+from __future__ import annotations
+
+import logging
+import os
+import sys
+
+
+def configure_logging() -> None:
+    level_name = os.environ.get("LOG_LEVEL", "INFO").upper()
+    level = getattr(logging, level_name, logging.INFO)
+
+    handler = logging.StreamHandler(sys.stderr)
+    handler.setFormatter(logging.Formatter("%(asctime)s %(levelname)-5s %(name)s: %(message)s"))
+
+    root = logging.getLogger()
+    root.setLevel(level)
+    root.handlers = [handler]