feat(commands): integrate standard CAD commands and fix behavior gaps

Broad pass over the command set: integrate missing commands, wire
previously-unreachable ribbon/menu buttons, and correct name/behaviour
mismatches. Every UI command token now resolves (real handler where the
infrastructure exists, an honest "not yet implemented" status otherwise).

New commands:
- Draw: 3DPOLY, 2D solid (SO/SOLID2D), HELIX, TRACE, SKETCH, DIMCENTER
  (DCE/CENTERMARK)
- Modify/inquiry: REVERSE, MEASUREGEOM (MEA), DBLIST
- Data/manage: BASE, OVERKILL (exact-duplicate removal), AUDIT (read-only
  integrity report), SETVAR (system-variable get/set), SCRIPT (.scr runner),
  FINDNONPURGEABLE

Behaviour fixes:
- LINE and SPLINE gain Close/Undo; AREA computes area/perimeter in f64
  (correct at large coordinates)
- ATTEDIT/ATE unified so the alias and the ribbon button open the
  interactive editor; -ATTEDIT is the command-line form
- Linear/aligned/radius/diameter dimensions gain a text override (Text) and
  text angle (Angle) option
- INSERT gains Scale/Rotate options; COPY gains an Array option
- LINETYPE SET sets the current entity linetype; SETBYLAYER resets overrides
- UNDO accepts a step count

Integrations: standard dimension/block aliases (DLI/DRA/DAN, BMAKE,
EXPORTPDF, DDIM), drafting-aid and screen toggles (GRID/SNAP/POLAR/OSNAP/
DSETTINGS/CLEANSCREEN/QUICKPROPERTIES), viewport tiling
(CASCADE/HORIZONTAL/VERTICAL/VPJOIN), and customization entry points
(CUI/ALIASEDIT).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/commands/view.rs

@@ -237,6 +237,13 @@ impl OpenCADStudio {
                 self.command_line.push_info("Opening release notes...");
             }
 
+            // ── CUI / ALIASEDIT — customization entry points ───────────────
+            // Command-alias and key-binding editing lives in the keyboard
+            // shortcuts panel, so route the customization verbs there.
+            "CUI" | "ALIASEDIT" => {
+                return Some(Task::done(Message::ShortcutsPanelOpen));
+            }
+
             // ── Keyboard Shortcuts panel ──────────────────────────────────
             cmd if cmd == "SHORTCUTS" || cmd.starts_with("SHORTCUTS ") => {
                 let raw_rest = cmd.trim_start_matches("SHORTCUTS").trim();
@@ -357,6 +364,15 @@ impl OpenCADStudio {
                 return Some(Task::done(Message::PspaceCommand));
             }
 
+            // ── Viewport arrangement shortcuts ────────────────────────────
+            // Tile the model viewports into preset splits. Each delegates to the
+            // matching VPORTS configuration so the Model/paper handling stays in
+            // one place.
+            "HORIZONTAL" => return self.dispatch_view("VPORTS 2H", i),
+            "VERTICAL" => return self.dispatch_view("VPORTS 2V", i),
+            "VPJOIN" => return self.dispatch_view("VPORTS SINGLE", i),
+            "CASCADE" => return self.dispatch_view("VPORTS 4", i),
+
             // ── VPORTS — list or create preset viewport configurations ────
             cmd if cmd == "VPORTS" || cmd.starts_with("VPORTS ") => {
                 let sub = cmd.split_whitespace().nth(1).unwrap_or("").to_uppercase();