Give every tab a headline; restore tab 3's section rule; drop the conditional

Tabs 2 and 3 each opened with a claim; tab 1 opened with instructions, so the
proposition the other two tabs attack was never stated. Tab 1 now opens with "A
working model that explains itself", making the sequence assert, undermine, what
survives.

Restores the horizontal rule before the conformal section -- present until v3.2,
where it sat where the chart needed to go and was not put back. After a figure, a
table and a blockquote, an h3 alone does not read as a section boundary.

Tab 3 label drops the conditional: "What We'd Show an Auditor" -> "What We Show an
Auditor".

Mirrors llm-wiki commit 18dcbd6.

app.py

@@ -172,6 +172,7 @@ with gr.Blocks(title="Explainable & Auditable Alloy Defect Detection",
     )
     with gr.Tab("1 - Classify & Explain"):
         gr.Markdown(
+            "### A working model that explains itself\n\n"
             "Upload a micrograph (or pick an example below). The model predicts the "
             "most likely defect class; the heatmap shows which pixels drove that "
             "prediction (**Grad-CAM**, implemented from first principles with PyTorch "
@@ -206,7 +207,7 @@ with gr.Blocks(title="Explainable & Auditable Alloy Defect Detection",
         )
         gr.Markdown(SPURIOUS_MARKDOWN)
 
-    with gr.Tab("3 - What We'd Show an Auditor"):
+    with gr.Tab("3 - What We Show an Auditor"):
         gr.Markdown(
             """
             ### First: can we even tell whether the heatmap is faithful?
@@ -240,6 +241,8 @@ with gr.Blocks(title="Explainable & Auditable Alloy Defect Detection",
             > why we treat this curve as supporting evidence rather than proof, and why the
             > guarantee below is what we would actually put in front of an auditor.
 
+            ---
+
             ### So what survives? Conformal Risk Control
 
             **Not covered anywhere in the course** — taken from Shen & Liu,