Page warnings log their line only, never words or source (M-11)

A document can forge both a console message and its source (KaTeX's
\errmessage, data: scripts, sourceURL, encoded paths), so the display
handler logs a line number and nothing the page wrote. The page's own
diagnostics reach the app over elyQuery: a missed reveal sends its
line; the visual failure and diagram lines already did. A test calls
the real handler and checks the captured log.

Round 5 found only the missing test; it is added and mutation-checked,
with no sixth review under the five-round cap. M-15 is new: the print
page runs a document's scripts.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/ely-mark/web/src/render.js

@@ -27,9 +27,8 @@ async function draw(tree) {
     try {
       const svg = await paint(node.value, 'paper')
       Object.assign(node, { type: 'html', value: `<figure class="diagram">${svg}</figure>` })
-    } catch (error) {
+    } catch {
       // Lines only: Mermaid's message quotes the document.
-      console.warn(`ely: a diagram did not draw: ${error.name}`)
       failed.push(node.position.start.line)
     }
   }