refactor(gui): split app.rs into models and panel modules

Extract types (models.rs), font settings, session controls, and send
panel into separate modules. Reduces app.rs from 1488 to 848 lines.
Zero behavior change.

- models.rs: ConnectionStatus, View, SendMode, LineEnding,
  DisplayOptions, SearchState, SessionTab
- panels/font_settings.rs: font selector and settings window
- panels/session_controls.rs: session connect/disconnect UI
- panels/send_panel.rs: send input and payload building

crates/pipeview-gui/src/panels/session_controls.rs

@@ -0,0 +1,147 @@
+use crate::models::{ConnectionStatus, SessionTab, View};
+use egui::TextEdit;
+use pipeview_client::SessionManager;
+use pipeview_core::transport::TransportConfig;
+
+pub fn render_search_bar(ui: &mut egui::Ui, tab: &mut SessionTab) {
+    if !tab.search.active {
+        return;
+    }
+    ui.horizontal(|ui| {
+        let response = ui.add(
+            TextEdit::singleline(&mut tab.search.query)
+                .hint_text("Search...")
+                .desired_width(200.0),
+        );
+        if tab.search.just_opened {
+            response.request_focus();
+            tab.search.just_opened = false;
+        }
+        if response.changed() {
+            let matches = match tab.view {
+                View::Text => tab.console.search(&tab.search.query, tab.search.case_sensitive),
+                View::Hex => tab.hex.search(&tab.search.query, tab.search.case_sensitive),
+                View::Plot => Vec::new(),
+            };
+            tab.search.matches = matches;
+            tab.search.current_match = 0;
+        }
+        if response.lost_focus() && ui.input(|i| i.key_pressed(egui::Key::Enter)) {
+            tab.search.next();
+        }
+
+        ui.label(format!(
+            "{}/{}",
+            tab.search.current_display(),
+            tab.search.match_count()
+        ));
+
+        if ui.button("▲").clicked() {
+            tab.search.prev();
+        }
+        if ui.button("▼").clicked() {
+            tab.search.next();
+        }
+
+        if ui.checkbox(&mut tab.search.case_sensitive, "Aa").changed() {
+            let matches = match tab.view {
+                View::Text => tab.console.search(&tab.search.query, tab.search.case_sensitive),
+                View::Hex => tab.hex.search(&tab.search.query, tab.search.case_sensitive),
+                View::Plot => Vec::new(),
+            };
+            tab.search.matches = matches;
+            tab.search.current_match = 0;
+        }
+
+        if ui.button("✕").clicked() {
+            tab.search.clear();
+        }
+    });
+}
+
+pub fn render_session_controls(
+    ui: &mut egui::Ui,
+    manager: &SessionManager,
+    tab: &mut SessionTab,
+) -> bool {
+    let mut auto_reconnect_changed = false;
+    ui.horizontal_wrapped(|ui| {
+        let connected = matches!(
+            tab.status,
+            ConnectionStatus::Connected | ConnectionStatus::Connecting
+        );
+        let connect_label = if connected { "Disconnect" } else { "Connect" };
+        if ui.button(connect_label).clicked() {
+            if let Some(handle) = manager.get(tab.id) {
+                if connected {
+                    tab.status = ConnectionStatus::Disconnected;
+                    tokio::spawn(async move {
+                        let _ = handle.disconnect().await;
+                    });
+                } else {
+                    tab.status = ConnectionStatus::Connecting;
+                    tokio::spawn(async move {
+                        let _ = handle.connect().await;
+                    });
+                }
+            } else {
+                tab.status = ConnectionStatus::Error(String::from("session not found"));
+            }
+        }
+
+        // if ui.button("Reconnect").clicked() {
+        //     if let Some(handle) = manager.get(tab.id) {
+        //         tab.status = ConnectionStatus::Connecting;
+        //         tokio::spawn(async move {
+        //             let _ = handle.reconnect().await;
+        //         });
+        //     } else {
+        //         tab.status = ConnectionStatus::Error(String::from("session not found"));
+        //     }
+        // }
+
+        if ui.button("Clear").clicked() {
+            tab.console.clear();
+            tab.hex.clear();
+            tab.plot.clear();
+            tab.send_status = Some(String::from("Cleared"));
+        }
+
+        let response = ui.checkbox(&mut tab.auto_reconnect, "Auto reconnect");
+        if response.changed() {
+            tab.session_config.auto_reconnect = tab.auto_reconnect;
+            auto_reconnect_changed = true;
+            if let Some(handle) = manager.get(tab.id) {
+                let enabled = tab.auto_reconnect;
+                tokio::spawn(async move {
+                    let _ = handle.set_auto_reconnect(enabled).await;
+                });
+            } else {
+                tab.status = ConnectionStatus::Error(String::from("session not found"));
+            }
+        }
+        if matches!(tab.status, ConnectionStatus::Connected)
+            && matches!(tab.session_config.transport, TransportConfig::Serial { .. })
+        {
+            let dtr_changed = ui.checkbox(&mut tab.dtr, "DTR").changed();
+            let rts_changed = ui.checkbox(&mut tab.rts, "RTS").changed();
+            if dtr_changed || rts_changed {
+                if let Some(handle) = manager.get(tab.id) {
+                    let dtr = tab.dtr;
+                    let rts = tab.rts;
+                    tokio::spawn(async move {
+                        if dtr_changed {
+                            let _ = handle.set_dtr(dtr).await;
+                        }
+                        if rts_changed {
+                            let _ = handle.set_rts(rts).await;
+                        }
+                    });
+                } else {
+                    tab.status = ConnectionStatus::Error(String::from("session not found"));
+                }
+            }
+        }
+    });
+    auto_reconnect_changed
+}