feat(inspector): port the terminal inspector

Ports ZIG/src/inspector (the Dear ImGui terminal inspector) as the
ghostty-inspector crate using dear-imgui-rs + dear-imgui-glow (imgui-rs
lacks a safe docking API): screen, modes, keyboard events, terminal IO
/ VT sequence log with filtering, cell inspector with picking, page
list, renderer and size/font info, with Ghostty's docking layout. The
crate denies unsafe except a single dock.rs module wrapping DockBuilder.

GTK: imgui_widget, inspector_widget and inspector_window classes with
their blueprints replace the former no-op; ctrl+shift+i toggles the
inspector window.

Core: activate/deactivate hooks, key event and mouse recording, and VT
stream recording in termio while an inspector is active, as in Zig;
overlay features reach the renderer through an InspectorHook on the
render state. The debug input replay hook gained inspector-screenshot/
click/scroll steps used to verify all tabs in the real app.

Deviations: font size scales with the display scale instead of Zig's
fixed 16*2; pop-out dock splits apply one frame later; DCS/APC
descriptions are approximated.

Test Plan:
- cargo test -p ghostty-inspector (15 incl. headless full-UI draw)
- cargo test -p ghostty-core --test e2e_inspector (4)

crates/ghostty-apprt-gtk/resources/ui/1.5/imgui-widget.blp

@@ -0,0 +1,51 @@
+using Gtk 4.0;
+using Adw 1;
+
+template $GhosttyImguiWidget: Adw.Bin {
+  styles [
+    "imgui",
+  ]
+
+  Adw.Bin {
+    Gtk.GLArea gl_area {
+      auto-render: true;
+      // needs to be focusable so that we can receive events
+      focusable: true;
+      focus-on-click: true;
+      allowed-apis: gl;
+      realize => $realize();
+      unrealize => $unrealize();
+      resize => $resize();
+      render => $render();
+
+      EventControllerFocus {
+        enter => $focus_enter();
+        leave => $focus_leave();
+      }
+
+      EventControllerKey {
+        key-pressed => $key_pressed();
+        key-released => $key_released();
+      }
+
+      GestureClick {
+        pressed => $mouse_pressed();
+        released => $mouse_released();
+        button: 0;
+      }
+
+      EventControllerMotion {
+        motion => $mouse_motion();
+      }
+
+      EventControllerScroll {
+        scroll => $scroll();
+        flags: both_axes;
+      }
+    }
+  }
+}
+
+IMMulticontext im_context {
+  commit => $im_commit();
+}