Switch remote deploy to vendored source builds

Move remote deployment to a vendored source bundle built on the target host via Docker so redeploys no longer require local cross-compilation or host Go installation.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

vendor/github.com/wailsapp/wails/v2/internal/shell/env.go

@@ -0,0 +1,40 @@
+package shell
+
+import (
+	"fmt"
+	"strings"
+)
+
+func UpsertEnv(env []string, key string, update func(v string) string) []string {
+	newEnv := make([]string, len(env), len(env)+1)
+	found := false
+	for i := range env {
+		if strings.HasPrefix(env[i], key+"=") {
+			eqIndex := strings.Index(env[i], "=")
+			val := env[i][eqIndex+1:]
+			newEnv[i] = fmt.Sprintf("%s=%v", key, update(val))
+			found = true
+			continue
+		}
+		newEnv[i] = env[i]
+	}
+	if !found {
+		newEnv = append(newEnv, fmt.Sprintf("%s=%v", key, update("")))
+	}
+	return newEnv
+}
+
+func RemoveEnv(env []string, key string) []string {
+	newEnv := make([]string, 0, len(env))
+	for _, e := range env {
+		if strings.HasPrefix(e, key+"=") {
+			continue
+		}
+		newEnv = append(newEnv, e)
+	}
+	return newEnv
+}
+
+func SetEnv(env []string, key string, value string) []string {
+	return UpsertEnv(env, key, func(_ string) string { return value })
+}