feat: implement TEXTEDIT command and TEXTEDITMODE system variable

- Adds TEXTEDIT command to seamlessly edit annotation objects in-place.
- Matches industry-standard CAD tools' prompt behavior and "Current settings" banner logic.
- Implements the TEXTEDITMODE system variable (0/1) for Multiple vs Single editing modes.
- Enhances command lifecycle with CmdResult::SuspendForTextEdit and post_editor_closed hooks, allowing commands to cleanly pause and resume after external UI editors close.

src/command/mod.rs

@@ -225,6 +225,12 @@ pub enum CmdResult {
     /// The host should look up the attdefs for `block_name` from the document
     /// and call `attreq_set_attdefs()` on the command, then loop on text input.
     AttreqNeeded { block_name: String },
+    /// Suspends command execution, moves it to suspended_cmd, and opens the text editor for the given handle.
+    SuspendForTextEdit { handle: Handle },
+    /// Requests a standard document-level undo while keeping the command active.
+    UndoDocument,
+    /// Sets the TEXTEDITMODE system variable and ends the command.
+    SetTexteditMode(bool),
 }
 
 /// What kind of value the active command is currently asking for. Drives
@@ -411,6 +417,11 @@ pub trait CadCommand: Send {
         false
     }
 
+    /// Called when the text editor closes, either because the user committed or cancelled the edit.
+    fn on_editor_closed(&mut self, _committed: bool) -> CmdResult {
+        CmdResult::Cancel
+    }
+
     /// Called when the user clicks and `needs_entity_pick()` is true.
     /// `handle` is the nearest wire's entity handle (Handle::NULL if nothing found).
     fn on_entity_pick(&mut self, _handle: Handle, _pt: Vec3) -> CmdResult {