add path mappings to translate jellyfin library paths to container mount paths

jellyfin may use different internal paths (e.g. /tv/) than container mounts
(/series/). path_mappings config (or PATH_MAPPINGS env var) translates at scan
time. configurable via setup ui or env var format: /tv/=/series/,/data/=/movies/

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/api/setup.ts

@@ -83,6 +83,12 @@ app.post('/subtitle-languages', async (c) => {
 	return c.json({ ok: true });
 });
 
+app.post('/path-mappings', async (c) => {
+	const body = await c.req.json<{ mappings: [string, string][] }>();
+	setConfig('path_mappings', JSON.stringify(body.mappings ?? []));
+	return c.json({ ok: true });
+});
+
 app.post('/clear-scan', (c) => {
 	const db = getDb();
 	db.prepare('DELETE FROM media_items').run();