refactor: rename content types to semantic taxonomy

- vault → notes (PKM-exported content)
- posts → articles (short-form, no TOC)
- papers → essays (long-form, with TOC)
- type: post → type: article (posts are just short articles)
- layouts/paper → layouts/essay
- 08a-paper.css → 08a-essay.css
- CSS: fix redundant li resets, remove role="main" from article,
  replace <small> prev/next labels, add console layout
- Update hugo.toml menus, internal URLs, front matter throughout
- Add docs/context.md, docs/css-refactor-plan.md

assets/css/layers/08-layout.css

@@ -208,6 +208,62 @@ nav[data-layout="actions"] a:hover {
   min-width: 0;
 }
 
+/* ── Console layout ─────────────────────────────────────────────────── */
+/* Docs variant: sidebar flush to the viewport left edge.               */
+/* No outer centering — grid spans full width, sidebar has no left gap. */
+
+[data-layout="console"] {
+  display: grid;
+  grid-template-columns: var(--sidebar-width) 1fr var(--toc-width);
+  grid-template-rows: auto;
+  gap: var(--space-6);
+  padding: var(--space-6) var(--space-5) var(--space-6) 0;
+  align-items: start;
+}
+
+[data-layout="console"] > nav[data-nav="sidebar"],
+[data-layout="console"] > aside[data-toc] {
+  position: sticky;
+  max-height: calc(100vh - var(--nav-height) - var(--space-4) * 2);
+  overflow-y: auto;
+  scrollbar-width: thin;
+  scrollbar-color: var(--border) transparent;
+}
+
+[data-layout="console"] > nav[data-nav="sidebar"] {
+  top: calc(var(--nav-height) + var(--space-4));
+  padding-inline: var(--space-3);
+}
+
+[data-layout="console"] > article {
+  min-width: 0;
+  max-width: none;
+}
+
+[data-layout="console"] > aside[data-toc] {
+  top: calc(var(--nav-height) + var(--space-8));
+  padding-top: var(--space-8);
+}
+
+@media (--docs-toc-hidden) {
+  [data-layout="console"] {
+    grid-template-columns: var(--sidebar-width) 1fr;
+  }
+  [data-layout="console"] > aside[data-toc] {
+    display: none;
+  }
+}
+
+@media (--md-n-below) {
+  [data-layout="console"] {
+    grid-template-columns: 1fr;
+    padding: var(--space-4);
+  }
+  [data-layout="console"] > nav[data-nav="sidebar"] {
+    display: none;
+  }
+}
+
 /* ── Grid helpers ───────────────────────────────────────────────────── */
 
 [data-layout="grid-2"] {