Add voice & video calling to any Flutter app FROM SCRATCH with the headless CometChat Calls SDK v5 (`cometchat_calls_sdk`, pub.dev) — no UI Kit. init→login→generateCallToken→joinSession, which hands back a Flutter `Widget?` you mount in your tree; CallSession listeners, in-call actions (mute/video/layout/record/PiP/raise-hand), meet-style session rooms AND 1:1 ringing (Chat SDK signaling + Calls SDK media). Triggers: 'add calling from scratch flutter', 'standalone video call dart', 'headless calls sdk flutter', 'build my own call screen flutter', 'meeting room join by session id flutter', 'one-on-one ringing call without uikit flutter'.
