[feat](trx-config): warn about deprecated configuration keys

Several keys quietly stopped doing what they look like they do, and nothing
said so: [remote] and the flat per-rig sections are ignored outright once
[[remotes]] / [[rigs]] exist, [frontends.rigctl].port and --rigctl-port have
been dead since rig_ports replaced them, [frontends.audio].rig_ports is
superseded by rig_urls, and default_rig_id was renamed to default_rig_name.

Warn once at load, naming the replacement.  Defaults are indistinguishable from
explicit values after deserialization, so the loader now records which key paths
the file actually set and the checks work off that — no warning for a setting
the user never wrote.

The single-rig flat layout is not deprecated: it is the documented simple form,
and only draws a warning when [[rigs]] is silently shadowing it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SyX26FCpMQxiBoC7r5K1A7
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-client/src/main.rs

@@ -20,6 +20,7 @@ use tokio::task::JoinHandle;
 use tracing::{error, info};
 
 use trx_app::{init_logging, normalize_name};
+use trx_config::ConfigFile;
 use trx_core::audio::AudioStreamInfo;
 
 use trx_core::decode::DecodedMessage;
@@ -80,7 +81,7 @@ struct Cli {
     /// rigctl frontend listen address
     #[arg(long = "rigctl-listen")]
     rigctl_listen: Option<IpAddr>,
-    /// rigctl frontend listen port
+    /// Deprecated: ignored, use [frontends.rigctl].rig_ports
     #[arg(long = "rigctl-port")]
     rigctl_port: Option<u16>,
     /// JSON TCP frontend listen address
@@ -127,6 +128,7 @@ fn check_config(loaded: &trx_config::ConfigLoad<ClientConfig>) -> DynResult<()>
     }
 
     let mut warnings: Vec<String> = loaded.unknown_keys.iter().map(|k| k.to_string()).collect();
+    warnings.extend(ClientConfig::deprecations(&loaded.present_keys));
 
     let mut cfg = loaded.config.clone();
     let mut errors = Vec::new();
@@ -223,6 +225,13 @@ async fn async_init() -> DynResult<AppState> {
         info!("Loaded configuration from {}", path.display());
     }
     loaded.report_unknown_keys(cli.strict_config)?;
+    loaded.report_deprecations();
+    if cli.rigctl_port.is_some() {
+        tracing::warn!(
+            "--rigctl-port is ignored; give each rig its own listener via \
+             [frontends.rigctl].rig_ports"
+        );
+    }
 
     let mut cfg = loaded.config;
     // Secrets configured as *_file are read before validation, so everything