fix(rag): do not mark a document indexed when no chunk could be embedded

With the embedding server unavailable every chunk failed, yet the document
was stored as indexed=true with 0 chunks, so the knowledge base listed it as
searchable while queries could never match it. The red use-case test caught
this; it had been written off as an environment failure.

Now a run with zero embedded chunks leaves indexed=false and throws
RAGEmbeddingFailed (surfaced by reindex, logged by addDocument).

Tests that only hold on the Windows developer machine now declare it: the
bundled SoX binary and PowerShell device discovery run on win32 only, and
the sidecar venv test runs only when sidecar/.venv exists. The Linux Forgejo
runner skips them instead of failing.

apps/desktop/tests/main/utils/paths.test.ts

@@ -37,13 +37,15 @@ describe('paths (dev)', () => {
     expect(getAppRoot()).toBe(desktopDir)
   })
 
-  it('prefers the bundled SoX binary over the system PATH', () => {
+  // resources/sox 에는 Windows용 sox.exe 만 커밋돼 있다(앱은 Windows 배포). 다른 OS에서는 PATH 의 sox 를 쓴다.
+  it.skipIf(process.platform !== 'win32')('prefers the bundled SoX binary over the system PATH', () => {
     expect(getSoxPath()).toContain(path.join('resources', 'sox', 'sox'))
     expect(existsSync(getSoxPath())).toBe(true)
     expect(getSoxPath()).not.toBe('sox')
   })
 
-  it('uses the sidecar virtualenv python when it exists', () => {
+  // 로컬 개발 환경에만 있는 sidecar/.venv 가 있을 때의 동작이다. CI 에는 venv 가 없다.
+  it.skipIf(!existsSync(path.join(desktopDir, 'sidecar', '.venv')))('uses the sidecar virtualenv python when it exists', () => {
     const launch = getSidecarCommand()
 
     expect(launch.source).toBe('venv')