refactor: replace legacy Config with Settings

Remove legacy src/config.rs and migrate all application consumers to
the nested Settings model. Baseliner, metrics, pingers, ratecontroller,
reflector selector, and main now use Settings. Derived min rates become
methods on NetworkSettings rather than stored legacy fields.
MeasurementType and ObservabilityProtocol move into the settings module.

src/baseliner.rs

@@ -5,10 +5,10 @@
 //
 // SPDX-License-Identifier: MPL-2.0
 
-use crate::Config;
 use crate::SHUTDOWN;
 use crate::metrics::{Metric, MetricsSender};
 use crate::pinger::PingReply;
+use crate::settings::Settings;
 use flume::{Receiver, Sender};
 use log::{debug, info};
 use std::collections::HashMap;
@@ -70,7 +70,7 @@ pub struct ControlSnapshot {
 }
 
 pub struct Baseliner {
-    pub config: Config,
+    pub settings: Settings,
     pub reselect_trigger: Sender<bool>,
     pub start_time: Instant,
     pub stats_rx: Receiver<PingReply>,
@@ -150,8 +150,14 @@ impl Baseliner {
     pub fn run(&self) -> anyhow::Result<()> {
         let mut reflectors = HashMap::<IpAddr, ReflectorState>::new();
 
-        let slow_factor = ewma_factor(self.config.tick_interval, BASELINE_HALF_LIFE_SECS);
-        let fast_factor = ewma_factor(self.config.tick_interval, RECENT_HALF_LIFE_SECS);
+        let slow_factor = ewma_factor(
+            self.settings.advanced_settings.tick_interval,
+            BASELINE_HALF_LIFE_SECS,
+        );
+        let fast_factor = ewma_factor(
+            self.settings.advanced_settings.tick_interval,
+            RECENT_HALF_LIFE_SECS,
+        );
 
         loop {
             if SHUTDOWN.load(Ordering::Relaxed) {
@@ -212,7 +218,7 @@ impl Baseliner {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::config::MeasurementType;
+    use crate::settings::MeasurementType;
     use std::time::Duration;
 
     fn state(