[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/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 {