Add native iOS app with App Store preparation

iOS app (ios/, SwiftUI, iOS 17+) in the web UI's styling with the Kamon
logo. It covers everything the web interface does except password, API
tokens and backups: dashboard, peers with search and filter, peer detail
with traffic charts, add/edit peers, one-time config with QR code and
share sheet, server settings with apply bar, app settings, data
retention and log viewer.

- Pairing by QR code or pasted pairing code; token kept in the keychain;
  self-signed certificates are pinned by SHA-256 fingerprint.
- Colour providers and logo drawing are nonisolated: SwiftUI's background
  renderer calls them, and main-actor closures crashed there when the
  camera scanner was open.
- App Store: version 1.0, export compliance, privacy manifest, app icon,
  release.sh (archive and upload), listing text, review notes and 6.9"
  screenshots in ios/AppStore.

Server:
- Full-access API tokens may use settings, logs and restart; password,
  tokens, backup/restore and the admin username stay admin-only.
- Web pairing dialog gains "Copy pairing code".
- The development simulator reports health checks in Linux wording.

Claude-Session: https://claude.ai/code/session_01RAnLbyQZ5ZTA7KqwXP98nw

api.go

@@ -125,14 +125,16 @@ func (a *App) routes() http.Handler {
 	g("POST /api/v1/peers/{id}/issue-config", a.issueConfig)
 	g("GET /api/v1/peers/{id}/stats", a.peerStats)
 
-	adm("GET /api/v1/settings", a.getSettings)
-	adm("PATCH /api/v1/settings", a.patchSettings)
-	adm("POST /api/v1/restart", a.restart)
+	// Full-access tokens (the iOS app) may change app settings and read logs.
+	// Password, tokens and backups stay with the admin account.
+	g("GET /api/v1/settings", a.getSettings)
+	g("PATCH /api/v1/settings", a.patchSettings)
+	g("POST /api/v1/restart", a.restart)
 	adm("GET /api/v1/tokens", a.listTokens)
 	adm("POST /api/v1/tokens", a.createToken)
 	adm("DELETE /api/v1/tokens/{id}", a.deleteToken)
-	adm("GET /api/v1/logs", a.logs)
-	adm("GET /api/v1/logs/download", a.downloadLog)
+	g("GET /api/v1/logs", a.logs)
+	g("GET /api/v1/logs/download", a.downloadLog)
 	adm("GET /api/v1/backup", a.backup)
 	adm("POST /api/v1/restore", a.restore)
 
@@ -816,6 +818,10 @@ func (a *App) patchSettings(w http.ResponseWriter, r *http.Request) {
 		writeErr(w, err)
 		return
 	}
+	if _, ok := m["adminUsername"]; ok && !who(r).IsAdmin {
+		writeJSON(w, http.StatusForbidden, map[string]string{"error": "only the admin account can change the username"})
+		return
+	}
 	var restart bool
 	err = a.store.Update(func(c *Config) error {
 		if err := field(m, "adminUsername", &c.Admin.Username); err != nil {