Refactor src/main.rs into modular src/app/ structure

Split the 4500-line main.rs into focused submodules under src/app/:
- mod.rs: H7CAD struct, Message enum, boot/new/run
- document.rs: DocumentTab, HistorySnapshot, HistoryState
- helpers.rs: pure helper functions
- history.rs: undo/redo logic
- properties.rs: properties panel logic
- layers.rs: layer sync
- commands.rs: dispatch_command
- cmd_result.rs: apply_cmd_result
- view.rs: view, subscription, tab bar
- update.rs: update message handler

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

src/ui/app_menu.rs

@@ -13,7 +13,7 @@ use iced::widget::{button, column, container, row, scrollable, text, text_input}
 use iced::{Background, Border, Color, Element, Length, Theme};
 use std::path::PathBuf;
 
-use crate::Message;
+use crate::app::Message;
 
 // ── Menu item definitions ─────────────────────────────────────────────────
 

src/ui/command_line.rs

@@ -1,6 +1,6 @@
 //! H7CAD-style command line — bottom panel with input and history
 
-use crate::Message;
+use crate::app::Message;
 use iced::widget::{column, container, row, text, text_input};
 use iced::{Background, Border, Color, Element, Length, Theme};
 

src/ui/layers.rs

@@ -1,7 +1,7 @@
 //! Layer Manager — floating window.
 
 use crate::ui::properties::{color_picker_dropdown, LinetypeItem, LwItem, lw_options};
-use crate::Message;
+use crate::app::Message;
 use acadrust::tables::layer::Layer as DocLayer;
 use acadrust::tables::Table;
 use acadrust::types::aci_table::aci_to_rgb;

src/ui/overlay.rs

@@ -9,7 +9,7 @@ use iced::{Background, Border, Color, Element, Length, Point, Size, Theme};
 
 use crate::scene::object::GripShape;
 use crate::scene::SelectionState;
-use crate::Message;
+use crate::app::Message;
 
 /// Half-size of the crosshair center square in screen pixels (square = SQ*2 × SQ*2).
 pub const CROSSHAIR_SQ: f32 = 7.5;

src/ui/properties.rs

@@ -22,7 +22,7 @@ const COMBO_PAD_V: f32   = (ROW_H - FONT_SZ * 1.3 - 2.0) / 2.0;  // fills combo
 const SWATCH_SZ: f32     = ROW_H * 0.54;                          // ≈14 px color swatch
 
 use crate::scene::object::{PropSection, PropValue};
-use crate::Message;
+use crate::app::Message;
 
 const VARIES_LABEL: &str = "*VARIES*";
 

src/ui/ribbon.rs

@@ -18,7 +18,7 @@ use iced::{Background, Border, Color, Element, Fill, Length, Padding, Theme};
 use crate::modules::registry;
 use crate::modules::{CadModule, IconKind, ModuleEvent, RibbonItem, ToolDef};
 use crate::ui::properties::{LwItem, LinetypeItem, acad_color_display, color_picker_dropdown, lw_options};
-use crate::Message;
+use crate::app::Message;
 
 // ── Layout constants ───────────────────────────────────────────────────────
 //

src/ui/snap_popup.rs

@@ -7,7 +7,7 @@ use iced::widget::{button, column, container, mouse_area, row, text};
 use iced::{Background, Border, Color, Element, Fill, Length, Padding, Theme};
 
 use crate::snap::{SnapType, Snapper, ALL_SNAP_MODES};
-use crate::Message;
+use crate::app::Message;
 
 /// Returns a full-screen overlay element:
 ///   - a transparent click-catcher that closes the popup on outside click

src/ui/statusbar.rs

@@ -5,7 +5,7 @@ use iced::widget::{button, container, row, text, tooltip, Row};
 use iced::{Background, Border, Color, Element, Length, Theme};
 
 use crate::snap::Snapper;
-use crate::Message;
+use crate::app::Message;
 
 #[derive(Clone, Default)]
 pub struct StatusBar {