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

content/vault/status.md

@@ -1,53 +0,0 @@
----
-title: "Status"
-description: "Render operational state with data-status — online, degraded, offline, unknown."
-section: vault
-prev-url: "wikilinks/"
-prev-title: "Wikilinks"
-next-url: "diff/"
-next-title: "Diff"
-type: vault
-date: 2026-04-09
-tags: ["vault", "status", "reference"]
-ai-disclosure: "generated"
-ai-model: "claude-sonnet-4-5"
-ai-provider: "Anthropic"
-
----
-
-## Overview
-
-Use `data-status` on any element to convey operational state. ASW renders a coloured indicator — no CSS classes required.
-
-```html
-<span data-status="online">API Gateway</span>
-<span data-status="degraded">Search Index</span>
-<span data-status="offline">Legacy Auth</span>
-<span data-status="unknown">Webhook Relay</span>
-```
-
-## Values
-
-| Value | Meaning | Indicator |
-|-------|---------|-----------|
-| `online` | Fully operational | Green dot |
-| `degraded` | Reduced capacity or elevated errors | Amber dot |
-| `offline` | Not reachable or deliberately down | Red dot |
-| `unknown` | State not yet determined | Grey dot |
-
-## Status Dashboard Pattern
-
-Combine with a `<dl>` for a compact service health panel:
-
-```html
-<dl>
-  <dt>API Gateway</dt>     <dd data-status="online">online</dd>
-  <dt>Search Index</dt>    <dd data-status="degraded">degraded</dd>
-  <dt>Webhook Relay</dt>   <dd data-status="offline">offline</dd>
-  <dt>Analytics</dt>       <dd data-status="unknown">unknown</dd>
-</dl>
-```
-
-## Usage Notes
-
-`data-status` is intentionally display-only — it carries no ARIA role. For accessibility, pair with visible text (as shown above) rather than relying on the colour dot alone.