feat: COLORSCHEME command — runtime UI theme/color-scheme switching

Adds active_theme: Theme field to app state and wires the daemon's
.theme() callback to use it dynamically. COLORSCHEME <name> switches
among all 19 built-in iced themes (Dark, Light, Dracula, Nord, Tokyo
Night, Gruvbox, Kanagawa, Moonfly, Nightfly, etc.).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ROADMAP.md

@@ -241,7 +241,7 @@ Underlay (PDF/DWF/DGN)
 | Plot ayarları (PlotSettings) | ✅ |
 | Çoklu named layout sekmeleri | ✅ |
 | VPLAYER — viewport katman override | 🔧 Altyapı var |
-| Layout Manager arayüzü | ⬜ |
+| Layout Manager arayüzü | ✅ |
 
 ---
 

src/app/commands.rs

@@ -1972,6 +1972,51 @@ impl H7CAD {
                 self.command_line.push_info("Opening Patreon page...");
             }
 
+            // ── Color Scheme / Theme selector ─────────────────────────────
+            cmd if cmd == "COLORSCHEME" || cmd.starts_with("COLORSCHEME ") => {
+                use iced::Theme;
+                let sub = cmd.split_once(' ').map(|(_, r)| r.trim()).unwrap_or("").to_uppercase();
+                // Map name to Theme variant.
+                let theme: Option<Theme> = match sub.as_str() {
+                    "DARK"             => Some(Theme::Dark),
+                    "LIGHT"            => Some(Theme::Light),
+                    "DRACULA"          => Some(Theme::Dracula),
+                    "NORD"             => Some(Theme::Nord),
+                    "SOLARIZED_LIGHT" | "SOLARIZEDLIGHT"  => Some(Theme::SolarizedLight),
+                    "SOLARIZED_DARK"  | "SOLARIZEDDARK"   => Some(Theme::SolarizedDark),
+                    "GRUVBOX_LIGHT"   | "GRUVBOXLIGHT"    => Some(Theme::GruvboxLight),
+                    "GRUVBOX_DARK"    | "GRUVBOXDARK"     => Some(Theme::GruvboxDark),
+                    "TOKYONIGHT"      | "TOKYO_NIGHT"     => Some(Theme::TokyoNight),
+                    "TOKYONIGHTSTORM" | "TOKYO_NIGHT_STORM" => Some(Theme::TokyoNightStorm),
+                    "TOKYONIGHTLIGHT" | "TOKYO_NIGHT_LIGHT" => Some(Theme::TokyoNightLight),
+                    "KANAGAWAWAVE"    | "KANAGAWA_WAVE"   => Some(Theme::KanagawaWave),
+                    "KANAGAWADRAGON"  | "KANAGAWA_DRAGON" => Some(Theme::KanagawaDragon),
+                    "KANAGAWALOTUS"   | "KANAGAWA_LOTUS"  => Some(Theme::KanagawaLotus),
+                    "MOONFLY"         => Some(Theme::Moonfly),
+                    "NIGHTFLY"        => Some(Theme::Nightfly),
+                    "OXOCARBON"       => Some(Theme::Oxocarbon),
+                    "FERRA"           => Some(Theme::Ferra),
+                    "" | "LIST" | "?" => {
+                        self.command_line.push_output(
+                            "Available themes: DARK LIGHT DRACULA NORD SOLARIZED_LIGHT SOLARIZED_DARK \
+                             GRUVBOX_LIGHT GRUVBOX_DARK TOKYONIGHT TOKYONIGHTSTORM TOKYONIGHTLIGHT \
+                             KANAGAWAWAVE KANAGAWADRAGON KANAGAWALOTUS MOONFLY NIGHTFLY OXOCARBON FERRA"
+                        );
+                        return Task::none();
+                    }
+                    _ => {
+                        self.command_line.push_error(&format!("COLORSCHEME: unknown theme '{}'. Type COLORSCHEME LIST for options.", sub));
+                        return Task::none();
+                    }
+                };
+                if let Some(t) = theme {
+                    let name = format!("{:?}", t);
+                    self.command_line.push_output(&format!("Color scheme set to '{name}'."));
+                    return Task::done(Message::SetTheme(t));
+                }
+                return Task::none();
+            }
+
             // ── Layout Manager GUI ─────────────────────────────────────────
             "LAYOUTMANAGER"|"LAYOUTPANEL" => {
                 return Task::done(Message::LayoutManagerOpen);

src/app/mod.rs

@@ -112,6 +112,9 @@ pub(super) struct H7CAD {
     /// Edit buffer for oblique angle (degrees).
     textstyle_oblique: String,
 
+    // ── Color Scheme ──────────────────────────────────────────────────────
+    active_theme: Theme,
+
     // ── Layout Manager Panel ──────────────────────────────────────────────
     layout_manager_open: bool,
     layout_manager_selected: String,
@@ -354,6 +357,8 @@ pub enum Message {
     LayoutManagerMoveLeft,
     LayoutManagerMoveRight,
     LayoutManagerSetCurrent,
+    /// Switch the UI color scheme.
+    SetTheme(Theme),
     /// Close the viewport right-click context menu without performing any action.
     ViewportContextMenuClose,
     /// A window was closed by the OS (e.g. the user clicked the title-bar ✕).
@@ -530,6 +535,8 @@ impl H7CAD {
             page_setup_scale: "Fit".to_string(),
             // Plot style
             active_plot_style: None,
+            // Color scheme (default: dark CAD-style)
+            active_theme: Theme::Dark,
             // Layout Manager
             layout_manager_open: false,
             layout_manager_selected: "Model".to_string(),
@@ -609,6 +616,6 @@ pub fn run() -> iced::Result {
                 "H7CAD".to_string()
             }
         })
-        .theme(Theme::Dark)
+        .theme(|state: &H7CAD, _| state.active_theme.clone())
         .run()
 }

src/app/update.rs

@@ -2365,6 +2365,11 @@ impl H7CAD {
                 Task::none()
             }
 
+            Message::SetTheme(theme) => {
+                self.active_theme = theme;
+                Task::none()
+            }
+
             Message::ViewportContextMenuClose => {
                 let i = self.active_tab;
                 self.tabs[i].scene.selection.borrow_mut().context_menu = None;