feat: initialize warpbox.dev project structure and backend

Initialize the repository with the core Go backend architecture and a frontend mockup for warpbox.dev, a self-hosted file-sharing application.

- Set up Go backend modules for configuration, HTTP server, middleware, handlers, and templates.
- Add local development scripts, environment templates, and basic project configuration.
- Include a React-based frontend mockup under the docs directory.

scripts/run/dev.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
+ENV_FILE="${ROOT_DIR}/scripts/env/dev.env"
+
+if [[ ! -f "${ENV_FILE}" ]]; then
+  echo "Missing ${ENV_FILE}. Create it from scripts/env/dev.env.example." >&2
+  exit 1
+fi
+
+set -a
+
+source "${ENV_FILE}"
+set +a
+
+cd "${ROOT_DIR}/backend"
+exec go run ./cmd/warpbox