o paper: add architecture figure; link in HTML and Markdown drafts

Author: Rajeev Jain

paper/images/architecture.svg

@@ -55,6 +55,8 @@ UXarray provides an Xarray-compatible interface for loading, analyzing, and visu
 
 ![Architecture overview](images/fig1.svg)
 
+![Architecture pipeline](images/architecture.svg)
+
 # Statement of need
 
 Modern climate and weather models increasingly use unstructured meshes. While Xarray offers labeled arrays and rich I/O, it does not natively understand unstructured grid topology. UXarray bridges this gap by enforcing a minimal UGRID-consistent contract and adding accessors that operate with mesh-aware semantics, enabling reproducible and scalable analysis pipelines.

paper/paper.md

@@ -71,6 +71,10 @@ major components.
   <img src="images/fig1.svg" alt="Overview diagram" width="640" />
   <figcaption>Figure 1: UXarray components and data flow.</figcaption>
 </figure>
+<figure>
+  <img src="images/architecture.svg" alt="Architecture diagram" width="800" />
+  <figcaption>Figure 2: Architecture: I/O → Grid → Accessors → Outputs.</figcaption>
+</figure>
 <pre><code>
 import uxarray as ux
 uxgrid = ux.open_grid("grid.ug")