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/test/README.md

@@ -0,0 +1,41 @@
+# Tests — helpers & midstate probes
+
+This short guide explains how to run the mid-typing (midstate) tests and regenerate parser probe output used by the test suite.
+
+Why
+- Mid-typing tests exercise the parser's provisional states (unclosed fences, loading links, emoji shortcodes, etc.).
+- When Vitest output is not fully available (CI or remote tooling), the probe script writes `test/probes/parse-output.json` so you can inspect the AST node shapes and tune tolerant assertions.
+
+Common commands (zsh / macOS)
+
+# Run the full test suite (CI mode):
+CI=1 pnpm test
+
+# Run only the midstate test file (verbose):
+CI=1 pnpm vitest run test/markdown-midstates.test.ts --reporter verbose
+
+# Run a named block/describe using grep (fast):
+pnpm vitest -t 'additional mid-state edge cases' --reporter verbose
+
+# Regenerate the probe JSON (writes to test/probes/parse-output.json):
+node test/probes/parse-probe-write-tmp.cjs
+
+# Inspect the probe output (first 200 lines):
+# macOS / zsh
+sed -n '1,200p' test/probes/parse-output.json
+
+Test helper notes
+- Use `test/utils/midstate-utils.ts` helpers instead of brittle JSON.stringify checks:
+  - `textIncludes(nodes, stringOrRegExp)` — safe recursive search (supports RegExp and raw strings)
+  - `collect(nodes, type)` — gather all nodes of a given type from an AST
+  - `hasLoadingLink(nodes)` and `links(nodes)` — helpers for link mid-states
+- Tests are intentionally tolerant: they prefer structured nodes when present but accept plain text fallback (useful when optional plugins are disabled).
+
+If you see a failing midstate test:
+1. Run the probe script to capture the parse AST for the failing input.
+2. Inspect `test/probes/parse-output.json` to see exactly which node fields exist (e.g. `text`, `raw`, `children`, `loading`).
+3. Adjust assertions to use `textIncludes(...)` or `collect(...)` to be tolerant of AST variations.
+
+If you'd like, I can:
+- Sweep tests for remaining fragile patterns and replace them conservatively in small batches (I already fixed the most obvious cases).
+- Add stricter/gated assertions behind an env var if you want deterministic enforcement in CI.