desktop: add pH calibration UI in Calibrate tab

cue/src/app.rs

@@ -998,6 +998,45 @@ impl App {
                     self.status = "No valid EIS data for Rs extraction".into();
                 }
             }
+            Message::PhCalKnownChanged(s) => { self.ph_cal_known = s; }
+            Message::PhAddCalPoint => {
+                if let Some(peak_mv) = crate::lsv_analysis::detect_qhq_peak(&self.lsv_points) {
+                    if let Ok(ph) = self.ph_cal_known.parse::<f32>() {
+                        self.ph_cal_points.push((ph, peak_mv));
+                        self.status = format!("pH cal point: pH={:.2} peak={:.1} mV ({} pts)",
+                            ph, peak_mv, self.ph_cal_points.len());
+                    }
+                } else {
+                    self.status = "No Q/HQ peak found in LSV data".into();
+                }
+            }
+            Message::PhClearCalPoints => {
+                self.ph_cal_points.clear();
+                self.status = "pH cal points cleared".into();
+            }
+            Message::PhComputeAndSetCal => {
+                if self.ph_cal_points.len() < 2 {
+                    self.status = "Need at least 2 calibration points".into();
+                } else {
+                    let n = self.ph_cal_points.len() as f32;
+                    let mean_ph: f32 = self.ph_cal_points.iter().map(|p| p.0).sum::<f32>() / n;
+                    let mean_v: f32 = self.ph_cal_points.iter().map(|p| p.1).sum::<f32>() / n;
+                    let num: f32 = self.ph_cal_points.iter()
+                        .map(|p| (p.0 - mean_ph) * (p.1 - mean_v)).sum();
+                    let den: f32 = self.ph_cal_points.iter()
+                        .map(|p| (p.0 - mean_ph).powi(2)).sum();
+                    if den.abs() < 1e-12 {
+                        self.status = "Degenerate calibration data".into();
+                    } else {
+                        let slope = num / den;
+                        let offset = mean_v - slope * mean_ph;
+                        self.ph_slope = Some(slope);
+                        self.ph_offset = Some(offset);
+                        self.send_cmd(&protocol::build_sysex_set_ph_cal(slope, offset));
+                        self.status = format!("pH cal set: slope={:.4} offset={:.4}", slope, offset);
+                    }
+                }
+            }
             Message::ClCalKnownPpmChanged(s) => { self.cl_cal_known_ppm = s; }
             Message::ClSetFactor => {
                 let known_ppm = self.cl_cal_known_ppm.parse::<f32>().unwrap_or(0.0);
@@ -1750,6 +1789,47 @@ impl App {
             ].spacing(10).align_y(iced::Alignment::End)
         );
 
+        /* pH calibration */
+        results = results.push(iced::widget::horizontal_rule(1));
+        results = results.push(text("pH Calibration (Q/HQ peak-shift)").size(16));
+        if let (Some(s), Some(o)) = (self.ph_slope, self.ph_offset) {
+            results = results.push(text(format!("slope: {:.4} mV/pH   offset: {:.4} mV", s, o)).size(14));
+            if let Some(peak) = crate::lsv_analysis::detect_qhq_peak(&self.lsv_points) {
+                if s.abs() > 1e-6 {
+                    let ph = (peak - o) / s;
+                    results = results.push(text(format!("Computed pH: {:.2}  (peak at {:.1} mV)", ph, peak)).size(14));
+                }
+            }
+        }
+        results = results.push(
+            row![
+                column![
+                    text("Known pH").size(12),
+                    text_input("7.00", &self.ph_cal_known)
+                        .on_input(Message::PhCalKnownChanged).width(80),
+                ].spacing(2),
+                button(text("Add Point").size(13))
+                    .style(style_action())
+                    .padding([6, 16])
+                    .on_press(Message::PhAddCalPoint),
+            ].spacing(10).align_y(iced::Alignment::End)
+        );
+        for (i, (ph, mv)) in self.ph_cal_points.iter().enumerate() {
+            results = results.push(text(format!("  {}. pH={:.2}  peak={:.1} mV", i + 1, ph, mv)).size(13));
+        }
+        results = results.push(
+            row![
+                button(text("Clear Points").size(13))
+                    .style(style_action())
+                    .padding([6, 16])
+                    .on_press(Message::PhClearCalPoints),
+                button(text("Compute & Set pH Cal").size(13))
+                    .style(style_action())
+                    .padding([6, 16])
+                    .on_press(Message::PhComputeAndSetCal),
+            ].spacing(10)
+        );
+
         row![
             container(inputs).width(Length::FillPortion(2)),
             iced::widget::vertical_rule(1),