fix(library): a failed import is reported, and the library is re-read either way

[mrsibe]

Fixes #146. A failed import used to produce nothing at all: no error, no row, and a panel that still showed its empty state — which reads as "the upload worked and the app is not showing it".

Two halves, both needed

The failure was discarded before it could be shown. SourcePanel calls the store and ignores what it returns:

for (const filePath of files) {
  await addDocumentFromFile(notebookId, filePath)   // { success, error } discarded
}

The store reports failure by returning { success: false, error } — the IPC layer already catches and describes it — so an unchecked return value makes a failure indistinguishable from a success. handleFileUpload, handleUrlImport, handleTextPaste and handleNoteImport all did this.

The list was only re-read when the import succeeded. KnowledgeService.addDocumentFromFile inserts the source row and then indexes it:

1. copy the file
2. parse it                    ← failure here: no row exists yet
3. insert the documents row     status 'processing'
4. indexDocument()             ← failure here: row is marked 'failed'

A failure at step 4 leaves a status: 'failed' row, and DocumentList already has the feedback for it — an alert saying the document failed to embed — but the list was never re-read, so the row never rendered and the alert never fired. A failure at step 2 (unsupported type, a corrupt or scanned file that extracts nothing) has no row at all and needs the message to say so.

What changes

• One rule for every entry point: an import attempt always ends by re-reading the library and recording the reason, and the reason reaches the reader as a toast (importFailed, en + zh).
• The rejection path re-reads too, deliberately: an IPC call can fail after the main process already wrote the source row, so the failure path cannot assume that nothing changed.
• The store's error state is now set from a failed result as well as from a thrown error — both are failures, and only the second one used to be recorded.

Not in this PR

• Recording an attempt that failed before its source row existed. An unparseable file still leaves no row; showing it as an ingestion record is [Feat] Ingestion runs: persistent pipeline state, retry, and non-destructive re-index #95.
• Any retry affordance. The re-index path exists but is not surfaced; [Feat] Ingestion runs: persistent pipeline state, retry, and non-destructive re-index #95 owns it.
• The hasEmbeddingModel gate that disables + — unrelated, and after fix(embedding): enable RAG with the built-in local model and batch local embeddings #134 the built-in local backend makes it effectively always open.

Behaviour note

The empty-note case used to alert() from a branch that could not be reached: the store returns { success: false } rather than throwing, so the catch never ran. It now shows the same message as a toast like every other import failure, and names the note instead of printing Note note_123 not found.

Verification

npm test	303 pass, 0 fail — 6 new in test/knowledgeStore.test.ts
npm run typecheck	clean (node, web, test)
npm run check:design	no violations
npx eslint <changed files>	0 problems
npm run build	bundles (renderer included)

The new tests drive all four entry points (pasted text, a file, a URL, a note) through the real store with a stubbed window.api, and assert three things per entry point: the failure is reported, the library is re-read (so a status: 'failed' row can appear), and the reason is recorded. Two more cover the success path clearing an earlier failure, and a rejected IPC call.

tsconfig.test.json now also includes src/preload/index.d.ts. Importing renderer code means typechecking it, and that file is where window.api is declared; without it a test cannot import a store that legitimately uses the preload global. The test file's header records why.

Not run: build:unpack + smoke:packaged — neither main nor preload changed (CI runs them for this PR, and they were run in #145 for the last main-process change). Not hand-verified: the toast itself, which needs the GUI. To check it by hand: Library → + → Upload file → pick a .zip or a scanned PDF → a red toast naming the file, instead of nothing happening.