[fix](trx-core): expose rig min tuning step and align UI tuning

Add min_freq_step_hz to RigCapabilities, set backend values, and make HTTP frontend parse suffix-less frequency input using the selected unit while snapping set/jog frequencies to rig step granularity.

Co-authored-by: Codex <codex@openai.com>
Signed-off-by: Stanislaw Grams <stanislawgrams@gmail.com>

src/trx-server/src/listener.rs

@@ -344,6 +344,7 @@ mod tests {
             model: "Dummy".to_string(),
             revision: "1".to_string(),
             capabilities: RigCapabilities {
+                min_freq_step_hz: 1,
                 supported_bands: vec![Band {
                     low_hz: 7_000_000,
                     high_hz: 7_200_000,

src/trx-server/trx-backend/src/dummy.rs

@@ -37,6 +37,7 @@ impl DummyRig {
                 model: "dummy".to_string(),
                 revision: "1.0".to_string(),
                 capabilities: RigCapabilities {
+                    min_freq_step_hz: 1,
                     supported_bands: vec![
                         Band {
                             low_hz: 1_800_000,

src/trx-server/trx-backend/trx-backend-ft450d/src/lib.rs

@@ -36,6 +36,7 @@ impl Ft450d {
             model: "FT-450D".to_string(),
             revision: "".to_string(),
             capabilities: RigCapabilities {
+                min_freq_step_hz: 10,
                 supported_bands: vec![
                     // Transmit-capable amateur bands (HF + 6m)
                     Band {

src/trx-server/trx-backend/trx-backend-ft817/src/lib.rs

@@ -37,6 +37,7 @@ impl Ft817 {
             model: "FT-817".to_string(),
             revision: "".to_string(),
             capabilities: RigCapabilities {
+                min_freq_step_hz: 10,
                 supported_bands: vec![
                     // Transmit-capable amateur bands
                     Band {