frontend: stop printing the paragraph position in the paper

Each heading carried a small chip with the paragraph's `sort` before its name.
That number is how a sentence is addressed and how a template switch lands
content on the right paragraph, but it is a writing detail: in the document it
is an implementation number sitting in the middle of the paper, in front of
every heading.

The reading view now prints the heading and nothing else. The editor keeps it
where it is acted on: the paragraph dialog names it in its title (`0 Abstract
sort = 1`), every sentence row carries its own `sort` input, and the 所属段落
select lists the positions to move between.

frontend/src/components/papers/PaperParagraph.vue

@@ -2,7 +2,7 @@
 /**
  * One paragraph of a paper, as the reader sees it.
  *
- * Two things about this component carry the feature's contracts:
+ * Three things about this component carry the feature's contracts:
  *
  * 1. **The structure is never skipped.** A paragraph with no sentences still
  *    renders its heading and a quiet placeholder, because the paper's shape
@@ -11,6 +11,10 @@
  *    `sort` order, one after another, with no separator added — Chinese
  *    sentences already end in punctuation, and inserting anything between them
  *    would show up in the text.
+ * 3. **Nothing but the writing is printed.** No position numbers, no ids, no
+ *    counts — this is the paper, not the editor. `sort` is a writing detail and
+ *    the places that show it are the paragraph dialog (its title and every
+ *    sentence row) and the list, which is where it is acted on.
  *
  * A sentence that quotes something gets a superscript marker numbered by the
  * paper's citation list, so the marker and the 参考文献 entry cannot disagree.
@@ -54,10 +58,11 @@ const anchor = computed(() => `paragraph-${props.paragraph.paper_template_filed_
 <template>
   <section :id="anchor" class="paragraph" :class="{ 'is-unset': !paragraph.matched }">
     <header class="paragraph-head">
+      <!-- The heading is the template's own text and nothing else. The
+           paragraph's position is a writing detail — the editor shows it, on
+           the dialog and beside every sentence — and printing it next to every
+           heading puts an implementation number in the middle of the paper. -->
       <h3 class="paragraph-title" :style="{ paddingLeft: headingIndent }">
-        <span class="paragraph-sort" :title="`sort = ${paragraph.paper_template_filed_sort}`">
-          {{ paragraph.paper_template_filed_sort }}
-        </span>
         <span v-if="paragraph.name" class="paragraph-name" :style="headingStyle">
           {{ paragraph.name }}
         </span>
@@ -156,21 +161,6 @@ const anchor = computed(() => `paragraph-${props.paragraph.paper_template_filed_
   line-height: 1.6;
 }
 
-/* The position the paragraph occupies in the document. Shown because it is
-   what a sentence is addressed by, and what survives a template switch. */
-.paragraph-sort {
-  flex: 0 0 auto;
-  min-width: 24px;
-  padding: 0 6px;
-  font-size: 11px;
-  font-weight: 400;
-  font-variant-numeric: tabular-nums;
-  text-align: center;
-  color: var(--el-text-color-secondary);
-  background-color: var(--el-fill-color);
-  border-radius: 4px;
-}
-
 .paragraph-name {
   min-width: 0;
   overflow-wrap: anywhere;