Top-level supervisor for the Arizona application.

Always supervises arizona_pubsub (the pg-based pubsub scope) and arizona_mcp_sup (the MCP session supervisor, which owns the session registry and starts per-session processes on demand), and owns the hot reloader's beam-facts cache table (arizona_reloader_consistency:create_table/0, created in init/1 so the cache outlives the short-lived processes that read it) and the dev MCP's log ring table (arizona_dev_log:create_table/0, for the same reason). Also supervises arizona_reloader_sup (one arizona_reloader_rule per rule) when the dev-mode reloader has rules in the reloader application env, and the configured server-side session store when the session_store env names a backend that exports child_spec/0 (e.g. arizona_session_store_ets). Live processes are not managed here -- they're started ad hoc by the transport layer (arizona_socket:init/4) and linked to the calling WebSocket process so they share its lifetime.

Reloader config

{arizona, [
    {reloader, #{
        enabled => true,
        watcher => arizona_watcher_fs,
        rules => [
            #{directory => "src",
              patterns => [".*\\.erl$"],
              callback => fun arizona_reloader:reload_erl/1}
        ]
    }}
]}

arizona_reloader_rule:child_specs/1 turns the rules into one rule process each, under arizona_reloader_sup, run by the watcher (an arizona_watcher implementation, from a dev-only dependency). Malformed config (missing directory or watcher, a watcher that is not on the code path) crashes the supervisor init so boot errors are obvious.