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 <[email protected]>

src/app/mod.rs

@@ -247,6 +247,9 @@ pub(super) struct OpenCADStudio {
     dyn_input: bool,
     /// Controls whether the TEXTEDIT command repeats automatically (0 = Multiple, 1 = Single).
     pub texteditmode: bool,
+    /// When true, a viewport right-click acts as Enter while a command is active
+    /// (idle right-click still opens the context menu). Toggled by `RMBENTER`.
+    pub rmb_enter: bool,
     /// Persisted default viewport background, restored from settings and applied
     /// to every drawing tab (new and opened) so a chosen background survives
     /// restarts (#188). `None` = the built-in dark-grey / off-white defaults.
@@ -1823,6 +1826,7 @@ impl OpenCADStudio {
             show_grid: false,
             dyn_input: true,
             texteditmode: false,
+            rmb_enter: false,
             default_bg_color: None,
             default_paper_bg_color: None,
             awaiting_vports: false,