log: send records natively to journald, keep stdout off-unit

A record written to stdout carries no priority, so journald files the
whole stream at one level and the swarm log store shows `info` whatever
level `tracing` gave it. Under a systemd unit the process's stdout
already *is* the journal, so the fix is to speak the journal protocol
directly and let each record carry its own severity.

New `hive-log` crate holds the one sink chooser, called by `hive-c0re`,
`hive-agent` and `swarm-controller`. It builds the same `EnvFilter`
those binaries always built, then installs exactly one layer — never
both, since a journald layer stacked on the `fmt` layer under a unit
stores every record twice.

The choice is an fstat compare, not a presence test: a child inherits
`$JOURNAL_STREAM` even when its own stdout was redirected elsewhere, so
the variable existing proves nothing. The crate parses `dev:inode` out
of it and compares both numbers against an fstat of stdout, the
descriptor the `fmt` layer writes to by default. No match, unset, or
unparseable takes the `fmt` branch. A journald layer that fails to
construct despite a match falls back to `fmt` and warns through it —
a process must never fail to start because of its logger.

swarm-controller/src/main.rs

@@ -1669,16 +1669,7 @@ fn keep_forge_for_state(
 
 #[tokio::main]
 async fn main() -> Result<()> {
-    tracing_subscriber::fmt()
-        .with_env_filter(
-            tracing_subscriber::EnvFilter::try_from_default_env()
-                .unwrap_or_else(|_| tracing_subscriber::EnvFilter::new("info")),
-        )
-        // This is a systemd-managed daemon — stdout always goes to journald,
-        // never a human terminal, and journald doesn't strip ANSI escapes:
-        // they land in victorialogs as raw byte-array spam otherwise.
-        .with_ansi(false)
-        .init();
+    hive_log::init();
 
     let path = socket_path();