feat(viewport): model-space tiled split (▤ / ▥ buttons)

Model layout artık tiled viewport destekliyor. Scene.model_tiles
normalized ekran rect'i + kamera tutan tile listesi; active_viewports
model layout'ta her tile için bir ViewportInstance üretiyor (aktif tile
canlı scene.camera'yı, inaktif tile'lar saklı snapshot'ı kullanıyor).

Render-mode picker'ın yanına iki buton eklendi: ▤ aktif tile'ı yatay
(üst/alt), ▥ dikey (sol/sağ) ikiye böler. split_active_model_tile
bölmeyi yapıyor; her iki yarı aktif kameranın kopyasını alıyor.

set_active_model_tile_at (cursor → aktif tile, kamera swap) ve
reset_model_tiles eklendi ama henüz bağlanmadı — aktif tile cursor
seçimi + pick yönlendirme sonraki adımda.

Co-Authored-By: Claude Opus 4.7 <[email protected]>

src/app/mod.rs

@@ -355,6 +355,9 @@ pub enum Message {
     CommandBackspace,
     /// TAB pressed: move focus to the next dynamic-input field (wraps).
     DynTabNext,
+    /// Split the active Model viewport in two. `true` → horizontal divider
+    /// (top / bottom); `false` → vertical divider (left / right).
+    SplitModelViewport(bool),
     /// Recall previous command in history (↑ arrow key).
     CommandHistoryPrev,
     /// Recall next command in history (↓ arrow key).

src/app/update.rs

@@ -916,6 +916,13 @@ impl OpenCADStudio {
                 self.focus_cmd_input()
             }
 
+            Message::SplitModelViewport(horizontal) => {
+                let i = self.active_tab;
+                self.tabs[i].scene.split_active_model_tile(horizontal);
+                self.tabs[i].scene.camera_generation += 1;
+                Task::none()
+            }
+
             Message::CommandHistoryPrev => {
                 // While autocomplete is showing suggestions, ↑ walks up
                 // that list. Otherwise it falls back to recall history.

src/app/view.rs

@@ -483,8 +483,54 @@ impl OpenCADStudio {
         // viewport drawing / selection is unaffected. In a paper layout
         // the active viewport gets its own picker (below) instead.
         if !is_paper && !tab.is_start {
+            // Render-mode picker + viewport-split buttons (horizontal /
+            // vertical divider of the active Model tile).
+            let split_btn = |glyph: &'static str, horizontal: bool| {
+                button(text(glyph).size(13).color(Color {
+                    r: 0.85,
+                    g: 0.85,
+                    b: 0.85,
+                    a: 1.0,
+                }))
+                .on_press(Message::SplitModelViewport(horizontal))
+                .padding([4, 8])
+                .style(|_: &Theme, status| iced::widget::button::Style {
+                    background: Some(Background::Color(match status {
+                        iced::widget::button::Status::Hovered => Color {
+                            r: 0.20,
+                            g: 0.20,
+                            b: 0.20,
+                            a: 0.85,
+                        },
+                        _ => Color {
+                            r: 0.10,
+                            g: 0.10,
+                            b: 0.10,
+                            a: 0.75,
+                        },
+                    })),
+                    border: Border {
+                        color: Color {
+                            r: 0.35,
+                            g: 0.35,
+                            b: 0.35,
+                            a: 1.0,
+                        },
+                        width: 1.0,
+                        radius: 4.0.into(),
+                    },
+                    text_color: Color {
+                        r: 0.85,
+                        g: 0.85,
+                        b: 0.85,
+                        a: 1.0,
+                    },
+                    ..Default::default()
+                })
+            };
+            let bar = row![info, split_btn("▤", true), split_btn("▥", false)].spacing(4);
             viewport_stack = viewport_stack.push(
-                container(iced::widget::opaque(info))
+                container(iced::widget::opaque(bar))
                     .width(Fill)
                     .height(Fill)
                     .align_x(iced::alignment::Horizontal::Left)