Restructure web app directories

pyproject.toml

@@ -36,6 +36,13 @@ dependencies = [
   "fastapi>=0.110",
   "uvicorn>=0.27",
   "pydantic>=2.5",
+  "openpyxl>=3.1",
+  "pyarrow>=15",
+]
+
+[project.optional-dependencies]
+dev = [
+  "httpx>=0.28",
 ]
 
 [project.urls]
@@ -51,11 +58,10 @@ include-package-data = true
 
 [tool.setuptools.packages.find]
 where = ["."]
-include = ["src*"]
+include = ["src*", "backend*"]
 
 [tool.setuptools.package-data]
 src = [
   "reference_data/*.json",
-  "gui/static/*",
   "skills/bundled/*/SKILL.md",
 ]