Port section layouts (docs, paper, vault) and papers content

- layouts/docs/single.html: docs section layout with sidebar nav + TOC
- layouts/paper/single.html: essay layout with byline, abstract, tags
- layouts/vault/single.html: vault layout with sidebar nav + front-matter prev/next
- content/papers/on-semantic-html.md: 'On Semantic HTML as Agent Interface'
- content/papers/on-sessional-continuity.md: 'On Sessional Continuity'

All layouts use partial nav.html for dynamic menus. Paper layout
uses data-paper, data-abstract, data-byline, data-role=tag-cloud.
36 pages build clean, paper pages live at /papers/.

Closes: asw#14, asw#10

hugo_stats.json

@@ -35,6 +35,7 @@
       "script",
       "section",
       "small",
+      "span",
       "strong",
       "sup",
       "table",
@@ -57,6 +58,7 @@
       "a-taxonomy-of-agency",
       "asw-data-attribute-vocabulary",
       "coda",
+      "conclusion",
       "craft-as-methodology",
       "example-full-page-skeleton",
       "fn:1",
@@ -67,10 +69,17 @@
       "fnref:3",
       "getting-started-with-asw-hugo",
       "installation",
+      "introduction",
       "principles-of-invisible-design",
+      "references",
+      "the-class-problem",
       "the-dorveille-principle",
       "the-economics-of-attention",
+      "the-problem-of-discontinuity",
       "the-table-of-hours",
+      "vocabulary-as-protocol",
+      "what-agents-need",
+      "what-persists",
       "what-we-subtract",
       "what-you-get"
     ]