chore(wailsv3): migrate Go backend from Wails v2 to v3

Minimal-structure migration to Wails v3.0.0-beta.20 (CLI-matching pin). Single App service preserved; no domain logic touched.

- main.go: wails.Run(options.App) -> application.New + RegisterService + Window.NewWithOptions. Window keeps title-with-version, 1024x768, RGBA background, Linux icon/translucency/GpuPolicyNever, ProgramName. SingleInstanceLock -> SingleInstanceOptions (same UniqueID); callback closes over the service variable set right after New.
- app.go: App holds *application.App instead of a context. startup(ctx) is gone; the version title moves into the window options via appTitle(). onSecondInstanceLaunch takes v3 SecondInstanceData (Args/WorkingDir) and uses Window.Current() Restore+Focus plus Event.Emit for launchArgs. ShowVersion uses Dialog.Info.
- AniList/MAL/Simkl *UserFunctions.go: runtime.BrowserOpenURL -> app.Browser.OpenURL (errors logged), runtime.MessageDialog -> app.Dialog.Info chains. OAuth callback servers, token flows, and key names unchanged.
- Secrets: 99designs/keyring replaced with zalando/go-keyring (what v3 itself depends on) under the same AniTrack service name, so existing stored tokens keep working. Per-file Set helpers kept; Open/Ready boilerplate deleted (zalando needs no handle).
- go.mod: v2 + 99designs dropped (stale v2 replace directive removed), v3 beta.20 + zalando v0.2.8 added.

go.mod

@@ -3,49 +3,22 @@ module AniTrack
 go 1.25.0
 
 require (
-	github.com/99designs/keyring v1.2.2
 	github.com/tidwall/gjson v1.19.0
-	github.com/wailsapp/wails/v2 v2.15.0
+	github.com/wailsapp/wails/v3 v3.0.0-beta.20
+	github.com/zalando/go-keyring v0.2.8
 )
 
 require (
-	git.sr.ht/~jackmordaunt/go-toast/v2 v2.0.3 // indirect
-	github.com/99designs/go-keychain v0.0.0-20191008050251-8e49817e8af4 // indirect
-	github.com/bep/debounce v1.2.1 // indirect
+	github.com/adrg/xdg v0.5.3 // indirect
+	github.com/coder/websocket v1.8.14 // indirect
 	github.com/danieljoos/wincred v1.2.3 // indirect
-	github.com/dvsekhvalnov/jose2go v1.8.0 // indirect
 	github.com/go-ole/go-ole v1.3.0 // indirect
-	github.com/godbus/dbus v0.0.0-20190726142602-4481cbc300e2 // indirect
 	github.com/godbus/dbus/v5 v5.2.2 // indirect
-	github.com/google/uuid v1.6.0 // indirect
-	github.com/gorilla/websocket v1.5.3 // indirect
-	github.com/gsterjov/go-libsecret v0.0.0-20161001094733-a6f4afe4910c // indirect
-	github.com/jchv/go-winloader v0.0.0-20250406163304-c1995be93bd1 // indirect
-	github.com/labstack/echo/v4 v4.15.2 // indirect
-	github.com/labstack/gommon v0.5.0 // indirect
-	github.com/leaanthony/go-ansi-parser v1.6.1 // indirect
-	github.com/leaanthony/gosod v1.0.4 // indirect
-	github.com/leaanthony/slicer v1.6.0 // indirect
-	github.com/leaanthony/u v1.1.1 // indirect
 	github.com/mattn/go-colorable v0.1.14 // indirect
 	github.com/mattn/go-isatty v0.0.22 // indirect
-	github.com/mtibben/percent v0.2.1 // indirect
-	github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c // indirect
-	github.com/pkg/errors v0.9.1 // indirect
-	github.com/rivo/uniseg v0.4.7 // indirect
-	github.com/samber/lo v1.53.0 // indirect
 	github.com/tidwall/match v1.2.0 // indirect
 	github.com/tidwall/pretty v1.2.1 // indirect
-	github.com/tkrajina/go-reflector v0.5.8 // indirect
-	github.com/valyala/bytebufferpool v1.0.0 // indirect
-	github.com/valyala/fasttemplate v1.2.2 // indirect
-	github.com/wailsapp/go-webview2 v1.0.23 // indirect
-	github.com/wailsapp/mimetype v1.4.1 // indirect
-	golang.org/x/crypto v0.53.0 // indirect
-	golang.org/x/net v0.56.0 // indirect
 	golang.org/x/sys v0.46.0 // indirect
-	golang.org/x/term v0.44.0 // indirect
-	golang.org/x/text v0.39.0 // indirect
 )
 
 // replace github.com/wailsapp/wails/v2 v2.9.1 => /home/nymusicman/go/pkg/mod