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/events/noemit_test.go

@@ -16,6 +16,13 @@ var allowedEmitters = map[string]bool{
 // TestNoDirectRuntimeEmits fails if anything outside backend/events
 // calls the Wails runtime's event emitter directly.
 //
+// The original reason was survival: v2's runtime.EventsEmit called
+// log.Fatalf on a context that did not carry the runtime, so a direct
+// call from a background worker could take the process down.  v3's
+// emit takes no context and cannot do that, and the rule is kept for
+// the weaker but still real reason — one emit path is what lets
+// emitStatus drop an unchanged payload for every caller at once.
+//
 // This is a text walk rather than a golangci-lint rule because
 // golangci-lint runs once per build configuration, so a call in an
 // indexbuild- or dev-tagged file is only seen by the pass that compiles
@@ -23,10 +30,11 @@ var allowedEmitters = map[string]bool{
 // entirely.
 func TestNoDirectRuntimeEmits(t *testing.T) {
 	// A selector, not a bare name: built at runtime so this file does
-	// not match itself, and qualified so it catches every import alias
-	// the tree uses (plain runtime., and wailsruntime.) without also
-	// matching an identifier that merely ends in the same letters.
-	needle := ".Events" + "Emit("
+	// not match itself, and qualified so it catches the call however
+	// the application value is named (app.Event.Emit, a.Event.Emit,
+	// application.Get().Event.Emit) without matching an identifier
+	// that merely ends in the same letters.
+	needle := ".Event" + ".Emit("
 
 	root := filepath.Join("..", "..")