feat: import a Calibre library

Reads metadata.db and copies the books into a library — from a zip uploaded on
the library settings page, or from a path with `litestar calibre-import`. The
source is never touched, and re-running only picks up what is new.

Also names the formats mimetypes does not know: a Calibre library is full of
MOBI and AZW3, and a null content type used to fail the book endpoint.

frontend/src/lib/api/calibre-import.remote.ts

@@ -0,0 +1,51 @@
+import { command, getRequestEvent, query } from '$app/server';
+import { error } from '@sveltejs/kit';
+
+import { stringCoerce } from '$lib/schema/common';
+import type { CalibreImport } from '$lib/schema/library';
+
+/** The backend's own message for a failed response, rather than its JSON envelope. */
+function detailOf(body: string): string {
+	try {
+		const parsed = JSON.parse(body);
+		return typeof parsed?.detail === 'string' ? parsed.detail : body;
+	} catch {
+		return body;
+	}
+}
+
+/**
+ * Where an import has got to.
+ *
+ * A `query` rather than a `command` so it can be refreshed, but it is polled on a timer
+ * rather than cached — the answer changes on its own.
+ *
+ * Starting an import is deliberately **not** here: the archive goes straight to the
+ * backend through the proxy, so it never passes through this process. See the import
+ * screen's `upload`.
+ */
+export const getCalibreImport = query(stringCoerce, async (jobId): Promise<CalibreImport> => {
+	const { locals } = getRequestEvent();
+
+	const response = await locals.api.get(`/libraries/imports/${jobId}`);
+
+	if (!response.ok) error(response.status, detailOf(await response.text()));
+
+	return await response.json();
+});
+
+/**
+ * Ask an import to stop after the book it is on.
+ *
+ * Not an abort: a book abandoned mid-copy would leave files on disk with no row
+ * describing them. Whatever it has imported stays imported.
+ */
+export const cancelCalibreImport = command(stringCoerce, async (jobId): Promise<CalibreImport> => {
+	const { locals } = getRequestEvent();
+
+	const response = await locals.api.delete(`/libraries/imports/${jobId}`);
+
+	if (!response.ok) error(response.status, detailOf(await response.text()));
+
+	return await response.json();
+});

frontend/src/lib/api/index.ts

@@ -2,6 +2,7 @@ export * from './auth.remote';
 export * from './author.remote';
 export * from './book.remote';
 export * from './bookshelf.remote';
+export * from './calibre-import.remote';
 export * from './library.remote';
 export * from './publisher.remote';
 export * from './tag.remote';