```plaintext
%% Notification Architecture (ADR-0021)
%% C4 Component diagram showing notification sources and hub

flowchart LR
    subgraph sources["📤 Notification Sources"]
        direction TB
        ci["🔧 Gitea Actions<br/>CI/CD builds"]
        alertmanager["🔔 Alertmanager<br/>Prometheus alerts"]
        gatus["❤️ Gatus<br/>Health monitoring"]
        flux["🔄 Flux<br/>GitOps events"]
    end

    subgraph hub["📡 Central Hub"]
        ntfy["📢 ntfy<br/>Notification Server"]
    end

    subgraph topics["🏷️ Topics"]
        direction TB
        t_ci["gitea-ci"]
        t_alerts["alertmanager-alerts"]
        t_gatus["gatus"]
        t_flux["flux"]
        t_deploy["deployments"]
    end

    subgraph consumers["📱 Consumers"]
        direction TB
        mobile["📱 ntfy App<br/>(iOS/Android)"]
        bridge["🌉 ntfy-discord<br/>Bridge"]
        discord["💬 Discord<br/>Webhooks"]
    end

    %% Source to hub
    ci -->|"POST"| ntfy
    alertmanager -->|"webhook"| ntfy
    gatus -->|"webhook"| ntfy
    flux -->|"notification-controller"| ntfy

    %% Hub to topics
    ntfy --> topics

    %% Topics to consumers
    t_ci --> mobile
    t_alerts --> mobile
    t_gatus --> mobile
    t_flux --> mobile
    t_deploy --> mobile

    topics --> bridge
    bridge --> discord

    classDef source fill:#3498db,color:white
    classDef hub fill:#e74c3c,color:white
    classDef topic fill:#9b59b6,color:white
    classDef consumer fill:#27ae60,color:white

    class ci,alertmanager,gatus,flux source
    class ntfy hub
    class t_ci,t_alerts,t_gatus,t_flux,t_deploy topic
    class mobile,bridge,discord consumer

```