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

docs/template-h1-title.md

@@ -0,0 +1,73 @@
+# Template Design: Handling the Markdown H1 / Front Matter Title Conflict
+
+## The Problem
+
+Standard markdown convention — Obsidian, agent-written files, generic `.md` — opens
+with a level-1 heading as the document title:
+
+```markdown
+# My Note Title
+
+Body text...
+```
+
+Hugo templates also render a title from front matter:
+
+```html
+<h1>{{ .Title }}</h1>
+```
+
+When both exist, the page gets two `<h1>` elements: one from the template,
+one from the rendered markdown content. The content one also carries an
+auto-generated `id` attribute from Hugo's heading anchor renderer.
+
+## The Two Template Contracts
+
+**Default (`_default/single.html`)** — bare markdown, minimal or no front matter.
+The `# Title` in content IS the h1. The template header renders only metadata
+(type, date, author, tags). No title rendered from front matter.
+
+**Vault (`vault/single.html`)** — enriched front matter (`title`, `type`, `date`,
+`author`, `tags`). Front matter `title` is authoritative. The `# Title` in content
+is still present (markdown convention) but must be suppressed.
+
+## The Fix: Engine-Agnostic Regex Strip
+
+When a template owns the title (renders `<h1>{{ .Title }}</h1>` from front matter),
+strip the first h1 from the rendered content before outputting it.
+
+**Hugo:**
+```
+{{ replaceRE "<h1[^>]*>.*?</h1>" "" .Content 1 | safeHTML }}
+```
+
+**Jinja2 / Flask:**
+```python
+import re
+content = re.sub(r'<h1[^>]*>.*?</h1>', '', content, count=1, flags=re.DOTALL)
+```
+
+**Nunjucks / Liquid / any engine:** equivalent string replace on the rendered HTML.
+
+This is a string operation on already-rendered HTML, not a template-engine concept.
+It ports to any engine without modification.
+
+## Why Not Other Approaches
+
+- **Author convention** (don't write `# Title` in vault files): breaks compatibility
+  with the entire markdown ecosystem.
+- **Hugo render hooks** (`layouts/vault/_markup/render-heading.html`): Hugo-specific,
+  not portable.
+- **CSS `display: none`**: h1 still exists in DOM — screen readers read it,
+  search engines index it. Semantically wrong.
+
+## Engine-Agnostic Principle
+
+ASW templates are prototyped in Hugo but must be portable to Flask/Jinja2 or
+any other engine. Template logic should express *what*, not *how*:
+
+- What: "strip h1 from content if front matter title is present"
+- How: engine-specific implementation of the same string operation
+
+Hugo-specific features (render hooks, shortcodes) are acceptable as prototyping
+tools but should not become load-bearing parts of the template design.