add tester ui, and restructure folders

shared/README.md

@@ -0,0 +1,21 @@
+# shared/
+
+Cross-function Python modules — the local equivalent of an AWS Lambda Layer.
+
+Anything in this directory is available to every function under
+`functions/<name>/handler.py` as a regular import:
+
+```python
+# functions/sign_pdfs/handler.py
+from shared import common_utils
+```
+
+The `shared/` directory is added to `sys.path` by the runner. For an AWS
+deploy, you'd either:
+
+1. Package it as a real Lambda Layer (preferred), and reference the layer ARN
+   from each function's deploy spec, **or**
+2. Vendor a copy into each function's deployment zip (simpler, less DRY).
+
+Currently empty — no cross-function code yet. First candidate would probably
+be a structured-logging helper once multiple functions need it.