Feat: ROADMAP Phase 1-5 batch — trim/extend, plot scale, viewport UX, mline caps, table alignment

- TRIM/EXTEND: Ray and XLine entities supported as cutting boundaries and trim targets;
  trim results in Ray→Line/Ray, XLine→Ray/Ray or Line; hover preview added
- Plot scale override: Fit/1:1/1:2/1:5/1:10/1:20/1:50/1:100/2:1 buttons added to Page Setup
  panel; PageSetupCommit applies scale to PlotSettings
- Viewport UX: locked viewport gets orange border; selected viewport gets white border
- Named view → viewport assignment: Choice dropdown in properties panel copies
  view_target/direction/height to the viewport entity
- MLine caps: perpendicular start/end cap lines added for open (non-closed) MLines
- Wipeout polygon grips: boundary vertices become editable grips when clipping_enabled+Polygonal;
  world→pixel back-projection on drag
- Table cell alignment: CellStyle.alignment (1-9) drives left/center/right + top/middle/bottom
  text positioning; cxf::measure_text() helper added
- New commands/features: DIMCONTINUE (DCO), DIMBASELINE (DBA), TOLERANCE (TOL), TABLE,
  ATTDEF, ATTEDIT, ATTDISP, BREAKATPOINT (BAP), PLOTWINDOW (PW), MLINE (ML);
  DIMSTYLE/DIMCURRENT/CLAYER/LTSCALE/CELTSCALE/SCALETEXT/XDATA/UCSICON/REGEN/DRAWORDER extended
- PLINE arc mode: A/L/CLOSE text input, bulge computation, arc preview
- Warning cleanup: removed unused imports and unreachable patterns

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

src/app/cmd_result.rs

@@ -573,6 +573,48 @@ impl H7CAD {
                     }
                 }
             }
+            CmdResult::SetPlotWindow { p1, p2 } => {
+                use acadrust::objects::{ObjectType, PlotSettings};
+                let layout_name = self.tabs[i].scene.current_layout.clone();
+                if layout_name == "Model" {
+                    self.command_line.push_error("PLOTWINDOW: switch to a paper space layout first.");
+                } else {
+                    let block_handle = self.tabs[i].scene.current_layout_block_handle_pub();
+                    let doc = &mut self.tabs[i].scene.document;
+                    let ps_handle = doc.objects.iter().find_map(|(h, obj)| {
+                        if let ObjectType::PlotSettings(ps) = obj {
+                            if ps.page_name == layout_name { Some(*h) } else { None }
+                        } else { None }
+                    });
+                    let ps_entry = match ps_handle {
+                        Some(h) => doc.objects.get_mut(&h),
+                        None => {
+                            let nh = acadrust::Handle::new(doc.next_handle());
+                            let ps = PlotSettings::new(layout_name.clone());
+                            doc.objects.insert(nh, ObjectType::PlotSettings(ps));
+                            doc.objects.get_mut(&nh)
+                        }
+                    };
+                    let _ = block_handle;
+                    if let Some(ObjectType::PlotSettings(ps)) = ps_entry {
+                        // Convert world-space points to DXF coordinates (X, Z plane → DXF X, Y).
+                        let x1 = p1.x.min(p2.x) as f64;
+                        let y1 = p1.z.min(p2.z) as f64;
+                        let x2 = p1.x.max(p2.x) as f64;
+                        let y2 = p1.z.max(p2.z) as f64;
+                        ps.set_plot_window(x1, y1, x2, y2);
+                        self.push_undo_snapshot(i, "PLOTWINDOW");
+                        self.tabs[i].dirty = true;
+                        self.command_line.push_output(&format!(
+                            "PLOTWINDOW: ({x1:.3},{y1:.3}) → ({x2:.3},{y2:.3})"
+                        ));
+                    }
+                }
+                self.tabs[i].active_cmd = None;
+                self.tabs[i].snap_result = None;
+                self.tabs[i].scene.clear_preview_wire();
+                self.restore_pre_cmd_tangent();
+            }
         }
         // Focus the command-line input while a command is active; blur it when the command ends.
         if self.tabs[i].active_cmd.is_some() {