feat(wails): move the Go side to v3

Phases 2 and 3 of plan 009, plus the parts of phase 1 that could not
land before them. Nothing in the tree imports wails/v2 any more; all
three lint and test configurations are green and `go build .` produces
a running binary.

The point of the migration is one file. backend/events/emit.go probed
ctx.Value("events") — a v2-*private* context key — to decide whether
emitting was safe, because runtime.EventsEmit called log.Fatalf on a
context without the runtime and took the process down with it. v3's
emit takes no context, so that is now application.Get() == nil. D1
held: events.Emit keeps its ctx as the WithSink test seam, and all 45
call sites and 7 test files are untouched.

The bootstrap splits into application.New + Window.NewWithOptions +
Run. Ten bound services implement ServiceStartup instead of being
handed a context by hand from OnStartup, which also stops ten
SetContext methods being exported as bindings. jobs.Registry and
explore.SearchIndex keep theirs — neither is bound, so converting them
would be churn for no binding removed.

Four things differed from the plan and are written up in it: GPU policy
moved to the per-window LinuxWindow options rather than surviving on
LinuxOptions; there is no OnStartup/OnDomReady option, so app-level
wiring hangs off ApplicationStarted; application.NewService is generic,
so FEBindings []any could not survive (the binding generator is a
static analyser and would have seen nothing); and the quit veto had to
be restructured, because v3's dialog answers on a callback rather than
returning the button, so ShouldQuit vetoes, asks, and quits again from
the callback.

Window state saving moves to a WindowClosing hook — the size has to be
read while the window still exists, and v3's OnShutdown has neither
context nor window. backend/logging is deleted rather than ported:
v3 takes a *slog.Logger directly, so the v2 logger.Logger adapter had
no caller left.

Phase 1's tail rides along, now that it can: the Makefile's wails
invocations, all 50 webkit2_41 sites, lefthook, both packaging recipes
and ci.yml's apt lists. v3 builds against GTK4 + WebKitGTK 6.0, which
Arch and ubuntu:24.04 both ship, so the tag is a deletion rather than
a translation.

Phase 4 is next and the branch is not usable until it lands: the app
builds, but frontend/wailsjs/ is v2's tree and nothing regenerates it,
so the frontend cannot reach the backend yet.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UDCbcCZQepnpSQYJ6SxxZm

backend/config/config.go

@@ -10,6 +10,7 @@ import (
 	"path"
 
 	"github.com/BurntSushi/toml"
+	"github.com/wailsapp/wails/v3/pkg/application"
 
 	"yellowjacket/backend/download"
 	"yellowjacket/backend/events"
@@ -280,9 +281,17 @@ func (c *Config) applyDefaults() {
 	c.Downloads.ApplyDefaults()
 }
 
-// SetContext sets the Wails runtime context for event emission.
-func (c *Config) SetContext(ctx context.Context) {
+// ServiceStartup is v3's service lifecycle hook: it runs once the
+// runtime exists, and ctx is cancelled when the app shuts down.  It
+// replaces v2's SetContext, which had to be called by hand from
+// OnStartup and was exported, so it was also bound to the frontend.
+func (c *Config) ServiceStartup(
+	ctx context.Context,
+	_ application.ServiceOptions,
+) error {
 	c.ctx = ctx
+
+	return nil
 }
 
 // GetLibraryDirectory returns the currently configured library directory path.

backend/config/emit_test.go

@@ -6,6 +6,8 @@ import (
 	"path/filepath"
 	"testing"
 
+	"github.com/wailsapp/wails/v3/pkg/application"
+
 	"yellowjacket/backend/events"
 )
 
@@ -28,7 +30,10 @@ func setupRecordedConfig(t *testing.T) (*Config, *events.Recorder) {
 	}
 
 	rec := events.NewRecorder()
-	conf.SetContext(events.WithSink(context.Background(), rec))
+	_ = conf.ServiceStartup(
+		events.WithSink(context.Background(), rec),
+		application.ServiceOptions{},
+	)
 
 	return conf, rec
 }