feat(jellyfin): add authenticated System/Info endpoint

Wire up GET /System/Info returning the previously unused dto.SystemInfo,
available to any authenticated user, matching real Jellyfin's authorization
(FirstTimeSetupOrIgnoreParentalControl, not admin-only). Feishin calls this
endpoint on connect and reads Version to feature-gate; it previously got the
unhandled-route 404.

The advertised version stays 10.8.13: Feishin unlocks structured lyrics and
public-playlist share permissions at >=10.9.0, and this API serves neither
(no lyrics endpoint; playlist user permissions are stubs), so a higher
version would falsely advertise capabilities.

server/jellyfin/README.md

@@ -115,7 +115,7 @@ favorites-only (`Filters=IsFavorite` or the standalone `isFavorite=true`); `Sort
 
 | Area | Endpoints |
 |---|---|
-| Handshake / system | `GET System/Info/Public`, `GET`/`POST System/Ping`, `GET QuickConnect/Enabled` |
+| Handshake / system | `GET System/Info/Public`, `GET System/Info` (authenticated), `GET`/`POST System/Ping`, `GET QuickConnect/Enabled` |
 | Auth | `POST Users/AuthenticateByName`, `GET Users/Public` |
 | Users | `GET UserViews`, `GET Users/{userId}/Views`, `GET Users/Me`, `GET Users/{userId}` |
 | Browsing | `GET Items`, `GET Users/{userId}/Items`, `GET Items/{itemId}`, `GET Users/{userId}/Items/{itemId}`, `GET Users/{userId}/Items/Latest`, `DELETE Items/{itemId}` (playlists only) |

server/jellyfin/api.go

@@ -92,6 +92,7 @@ func (api *Router) routes() http.Handler {
 		// Subsonic's getPlayer, so Jellyfin clients show up in the players list (and scrobbling has a
 		// player) even before the first playback report.
 		r.Use(api.withPlayer)
+		r.Get("/system/info", api.getSystemInfo)
 		r.Get("/userviews", api.getUserViews)
 		r.Get("/users/{userId}/views", api.getUserViews)
 		r.Get("/users/me", api.getCurrentUser)

server/jellyfin/e2e/system_test.go

@@ -30,6 +30,27 @@ var _ = Describe("System", func() {
 		})
 	})
 
+	Describe("GET /System/Info", func() {
+		It("returns system info to any authenticated user, matching the public Version", func() {
+			w := getAs(regularUser, "/System/Info")
+			var info map[string]any
+			parseInto(w, &info)
+			Expect(info["Version"]).ToNot(BeEmpty())
+			Expect(info["SupportsLibraryMonitor"]).To(BeTrue())
+
+			pub := rawReq("GET", "/System/Info/Public", "")
+			var pubInfo map[string]any
+			parseInto(pub, &pubInfo)
+			Expect(info["Version"]).To(Equal(pubInfo["Version"]))
+			Expect(info["Id"]).To(Equal(pubInfo["Id"]))
+		})
+
+		It("rejects unauthenticated requests", func() {
+			w := rawReq("GET", "/System/Info", "")
+			Expect(w.Code).To(Equal(http.StatusUnauthorized))
+		})
+	})
+
 	Describe("GET/POST /System/Ping", func() {
 		It("answers GET with a plain-text server name", func() {
 			w := rawReq("GET", "/System/Ping", "")

server/jellyfin/system.go

@@ -83,6 +83,13 @@ func (api *Router) getPublicSystemInfo(w http.ResponseWriter, r *http.Request) {
 	api.ok(w, r, api.publicInfo(r))
 }
 
+func (api *Router) getSystemInfo(w http.ResponseWriter, r *http.Request) {
+	api.ok(w, r, dto.SystemInfo{
+		PublicSystemInfo:       api.publicInfo(r),
+		SupportsLibraryMonitor: true,
+	})
+}
+
 // ping answers /System/Ping with a bare plain-text server name (not JSON-quoted): Jellyfin's
 // server does this and clients parse the raw body.
 func (api *Router) ping(w http.ResponseWriter, r *http.Request) {

server/jellyfin/system_test.go

@@ -38,6 +38,27 @@ var _ = Describe("System", func() {
 		Expect(info.ServerName).To(HavePrefix("Navidrome"))
 	})
 
+	It("returns authenticated system info with the public fields plus library monitor support", func() {
+		DeferCleanup(configtest.SetupConfig())
+		conf.Server.Jellyfin.ServerName = ""
+
+		w := httptest.NewRecorder()
+		r := httptest.NewRequest("GET", "/System/Info", nil)
+		api.getSystemInfo(w, r)
+
+		Expect(w.Code).To(Equal(http.StatusOK))
+		Expect(w.Header().Get("Content-Type")).To(ContainSubstring("application/json"))
+		var info dto.SystemInfo
+		Expect(json.Unmarshal(w.Body.Bytes(), &info)).To(Succeed())
+		Expect(info.Id).ToNot(BeEmpty())
+		Expect(info.Version).To(Equal(jellyfinVersion))
+		Expect(info.ProductName).To(Equal("Jellyfin Server"))
+		Expect(info.ServerName).To(HavePrefix("Navidrome"))
+		Expect(info.SupportsLibraryMonitor).To(BeTrue())
+		Expect(info.HasPendingRestart).To(BeFalse())
+		Expect(info.IsShuttingDown).To(BeFalse())
+	})
+
 	It("advertises a LocalAddress with the request scheme, host and Jellyfin base path", func() {
 		DeferCleanup(configtest.SetupConfig())