feat: Plot Style Table Editor GUI (PLOTSTYLEPANEL / STYLESMANAGER)

Opens a panel overlay showing all 255 ACI entries with their current
overrides (color, lineweight, screening). Allows editing entries
interactively, creating a new identity table when none is loaded,
and saving the modified table back to a CTB/STB file.

Commands: PLOTSTYLEPANEL, PLOTSTYLEEDITOR, STYLESMANAGER

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

src/app/commands.rs

@@ -3579,6 +3579,11 @@ impl H7CAD {
                 return Task::done(Message::StlExport);
             }
 
+            // ── Plot Style Editor GUI ─────────────────────────────────────
+            "PLOTSTYLEPANEL"|"PLOTSTYLEEDITOR"|"STYLESMANAGER" => {
+                return Task::done(Message::PlotStylePanelOpen);
+            }
+
             // ── Plot / Page Setup ──────────────────────────────────────────
             "PRINT"|"PLOT"|"EXPORT" => {
                 return Task::done(Message::PlotExport);