feat(desktop): embed BoosAPI Desktop client as a subproject

Vendor the rebranded BoosAPI Desktop client (Tauri + Vue) into metapi as
a monorepo subdirectory under desktop/. Source only — node_modules,
dist, Cargo target and the upstream .git history are excluded.

desktop/ keeps its own independent Cargo workspace (desktop/src-tauri
with crates/*); it is not part of the backend boosapi crate, so a
`cargo check` at the metapi root still compiles only the backend. Build
the desktop app from desktop/src-tauri per desktop/README.md.

Note: app icons are still placeholder assets pending the final BoosAPI
logo. The updater signing keys live outside the repo and are not
included.

desktop/libs/markstream-vue/docs/guide/api.md

@@ -0,0 +1,120 @@
+---
+description: Reference the low-level markstream-vue API for parser helpers, render-pipeline decisions, scoped overrides, and AST-aware integration points.
+---
+
+# API Reference
+
+This page covers the low-level entry points behind `markstream-vue`: parser helpers, render-pipeline decisions, and scoping hooks.
+
+If you are trying to look up exported Vue components such as `MarkdownRender`, `CodeBlockNode`, or `ImageNode`, use [Renderer & Node Components](/guide/components) instead. Pair this page with [Usage](/guide/usage) and [Props](/guide/props) when wiring everything together.
+
+## Render pipeline at a glance
+
+```
+Markdown string → getMarkdown() → markdown-it-ts instance
+            ↓
+   parseMarkdownToStructure(content, md) → AST (BaseNode[])
+            ↓
+   <MarkdownRender> → node components (CodeBlockNode, ImageNode, …)
+```
+
+You can jump in at any stage:
+- Provide `content` to let the component handle parsing automatically.
+- Provide `nodes` when you need full control over the AST (server-side parsing, custom transforms).
+
+## Parser helpers
+
+| Helper | Purpose | When to use |
+| ------ | ------- | ----------- |
+| `getMarkdown(msgId?, options?)` | Returns a configured `markdown-it-ts` instance with the plugins this package expects. | Customize parser options (HTML toggles, additional plugins) before transforming tokens. |
+| `parseMarkdownToStructure(content, md)` | Generates the AST consumed by `MarkdownRender` from a Markdown string. | Pre-parse on the server, run validations, or reuse the AST across renders. |
+
+Both helpers are framework-agnostic and can run in Node or the browser. For large documents you can reuse the `md` instance between parses to avoid re-initializing plugins.
+
+## Custom components & scoping
+
+Use `setCustomComponents(customId?, mapping)` to override any node renderer. Pair it with the `custom-id` prop on `MarkdownRender` so replacements stay scoped.
+
+```ts twoslash
+import type { Component } from 'vue'
+import { setCustomComponents } from 'markstream-vue'
+
+declare const CustomImageNode: Component
+
+setCustomComponents('docs', {
+  image: CustomImageNode,
+})
+```
+
+```vue twoslash
+<script setup lang="ts">
+import MarkdownRender from 'markstream-vue'
+
+const md = '![demo](https://example.com/demo.png)'
+</script>
+
+<template>
+  <MarkdownRender custom-id="docs" :content="md" />
+</template>
+```
+
+Tips:
+- Use descriptive IDs (`docs`, `playground`, `pdf-export`) for tracing.
+- Call `setCustomComponents(mapping)` to set globals, but prefer scoped IDs to avoid surprises in multi-instance apps.
+- Clean up mappings in SPA routers if you register them dynamically.
+
+## Parse hooks & transforms
+
+When passing `content`, you can intercept parser stages through `parse-options` (prop) or the `ParseOptions` parameter of `parseMarkdownToStructure`.
+
+Hooks:
+- `preTransformTokens(tokens)` — mutate tokens before default handling.
+- `postTransformTokens(tokens)` — inspect/adjust tokens before node generation.
+
+If you need to reshape the AST, post-process the returned nodes and pass them to `MarkdownRender` via `nodes`.
+
+Example: render AI “thinking” tags as custom components (no hooks needed):
+
+```ts twoslash
+import type { Component } from 'vue'
+import { setCustomComponents } from 'markstream-vue'
+
+declare const ThinkingNode: Component
+
+setCustomComponents('docs', { thinking: ThinkingNode })
+```
+
+```vue twoslash
+<script setup lang="ts">
+import MarkdownRender from 'markstream-vue'
+
+const doc = '<thinking>Need a plan</thinking>'
+</script>
+
+<template>
+  <MarkdownRender
+    custom-id="docs"
+    :custom-html-tags="['thinking']"
+    :content="doc"
+  />
+</template>
+```
+
+Hooks remain useful if you want to reshape the emitted `thinking` node (strip wrappers, remap attrs, merge blocks, etc.), or post-process the parsed nodes before rendering.
+
+## Utility exports
+
+Besides the core renderer and parser helpers, the package exposes:
+
+- `CodeBlockNode`, `MarkdownCodeBlockNode`, `MermaidBlockNode`, `MathBlockNode`, `ImageNode`, etc. — see [Components](/guide/components) for their props and CSS requirements.
+- `VueRendererMarkdown` (global component plugin) and shared type exports (component prop interfaces, parser types).
+
+For parser types and hooks, see [/guide/parser-api](/guide/parser-api) (or the `stream-markdown-parser` README on npm).
+
+## Styling + troubleshooting reminders
+
+- Always include a reset before `markstream-vue/index.css` and wrap it with `@layer components` when using Tailwind or UnoCSS. See the [Tailwind guide](/guide/tailwind) and the [CSS checklist](/guide/troubleshooting#css-looks-wrong-start-here).
+- Code/graph peers: KaTeX needs its own CSS import; Mermaid does not. Missing KaTeX styles often manifest as invisible formulas.
+- Use `custom-id` to scope overrides and avoid global selector conflicts.
+
+Need more examples? Jump into the [Playground](/guide/playground) or run `pnpm play` locally to experiment with custom parsers and renderers.