Rebrand CommGate to gsmnode and adopt new design system

Rename the whole project from CommGate to gsmnode and re-skin every
surface onto the new signal-green + ink design system (Space Grotesk /
IBM Plex Sans / JetBrains Mono, flat surfaces, two-arrow routing mark,
lowercase gsm+node wordmark).

- Web App + API panel: rewrite token layer, gn-* utilities, data-gsm-theme,
  new logo/favicon assets; both builds verified.
- Phone App (Flutter): green theme, new mark/wordmark widgets, adaptive
  launcher icons; rename Android applicationId/package to app.gsmnode.phone;
  bump AGP to 8.6.0 and google_fonts to 8.1.0; debug APK build verified.
- API Server (Go): panel routes, User-Agent, health service id, branding.
- Home Assistant Plugin: rename integration domain sms_gateway to gsmnode
  (folder, DOMAIN, services, entity ids, classes); py_compile verified.
- Update all READMEs; add .gitignore (excludes Design/, build artifacts).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

API Server/internal/api/util.go

@@ -0,0 +1,65 @@
+package api
+
+import (
+	"net/http"
+	"strconv"
+)
+
+// asString coerces an arbitrary JSON value to a string.
+func asString(v any) string {
+	switch t := v.(type) {
+	case string:
+		return t
+	case nil:
+		return ""
+	default:
+		return ""
+	}
+}
+
+// asInt coerces a JSON number/string to an int.
+func asInt(v any) int {
+	switch t := v.(type) {
+	case float64:
+		return int(t)
+	case int:
+		return t
+	case string:
+		if n, err := strconv.Atoi(t); err == nil {
+			return n
+		}
+	}
+	return 0
+}
+
+// asStringSlice coerces a JSON array (or single string) to []string.
+func asStringSlice(v any) []string {
+	switch t := v.(type) {
+	case []any:
+		out := make([]string, 0, len(t))
+		for _, e := range t {
+			if s, ok := e.(string); ok {
+				out = append(out, s)
+			}
+		}
+		return out
+	case []string:
+		return t
+	case string:
+		if t == "" {
+			return nil
+		}
+		return []string{t}
+	}
+	return nil
+}
+
+// queryInt parses a query parameter as an int, falling back to def.
+func queryInt(r *http.Request, key string, def int) int {
+	if v := r.URL.Query().Get(key); v != "" {
+		if n, err := strconv.Atoi(v); err == nil {
+			return n
+		}
+	}
+	return def
+}