feat(viewport): RMB=Enter option + timed right-click

Adds a configurable right-mouse-button behavior without disturbing orbit
or the context menu.

- New persisted setting `rmb_enter` (command `RMBENTER [ON|OFF]`, default
  off): when on, a right-click while a command is active acts as Enter
  (commit/close); when idle it still opens the context menu. Right-drag
  always orbits, so nothing is lost.
- Right-click vs orbit is now time-based: orbit engages only after the
  button is held >=150ms and the pointer moves, so a quick right-click is
  no longer swallowed by slight pointer jitter (was an 8px distance gate).
- The right-click Repeat menu now lists commands from every source
  (command line, ribbon, context menu, shortcuts) via a unified
  recents list recorded at the dispatch choke point, instead of only
  typed commands.

Closes #185

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

src/app/update/file.rs

@@ -40,6 +40,7 @@ impl OpenCADStudio {
             },
             plugin_repos: self.plugin_repos.clone(),
             texteditmode: self.texteditmode,
+            rmb_enter: self.rmb_enter,
             bg_color: self.default_bg_color.map(f4_to_u3),
             paper_bg_color: self.default_paper_bg_color.map(f4_to_u3),
         }
@@ -58,6 +59,7 @@ impl OpenCADStudio {
         self.disabled_plugins = s.disabled_plugins.iter().cloned().collect();
         self.plugin_repos = s.plugin_repos.clone();
         self.texteditmode = s.texteditmode;
+        self.rmb_enter = s.rmb_enter;
         self.default_bg_color = s.bg_color.map(u3_to_f4);
         self.default_paper_bg_color = s.paper_bg_color.map(u3_to_f4);
         // Push the restored background onto every drawing tab that exists now