Restructure examples directory and improve document storage (#189)

* Consolidate tests/ into examples/documents/

* Add line_count and reorder structure keys

* Lazy-load documents with _meta.json index

* Update demo script and add pre-shipped workspace

* Extract shared helpers for JSON reading and meta entry building

examples/workspace/_meta.json

@@ -0,0 +1,9 @@
+{
+  "12345678-abcd-4321-abcd-123456789abc": {
+    "type": "pdf",
+    "doc_name": "attention-residuals.pdf",
+    "doc_description": "This document introduces \"Attention Residuals\" (AttnRes) and its scalable variant \"Block AttnRes,\" novel mechanisms for replacing fixed residual accumulation in neural networks with learned, input-dependent depth-wise attention, addressing limitations of standard residual connections while optimizing memory, computation, and scalability for large-scale training and inference.",
+    "page_count": 21,
+    "path": "../documents/attention-residuals.pdf"
+  }
+}