feat(input): scalar entry via dynamic input

Text-input steps (OFFSET distance, POLYGON sides, radii, counts) were
swallowed by the dynamic-input overlay: typed digits landed in the field
buffer and Enter committed a point pick, so the value never reached
on_text_input (issue #61). Now each text step shows one scalar box whose
value routes to on_text_input on commit; non-numeric prompts (names,
keywords) keep going to the command line so mixed text like "Bolt12"
isn't split.

OFFSET reworked: object first, then through-mode by default — the offset
follows the cursor at the perpendicular distance to the object. Typing a
number locks the magnitude (cursor then only picks the side); a value
typed and clicked without Enter is applied before the point pick.

The dynamic-input overlay and the command line now show the active
step's prompt and hold it until the step completes.

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

src/app/commands.rs

@@ -1734,10 +1734,7 @@ impl OpenCADStudio {
                         self.tabs[i].scene.document.get_entity(h).cloned()
                     })
                     .collect();
-                let new_cmd = OffsetCommand::new(
-                    crate::modules::home::defaults::get_offset_dist(),
-                    all_entities,
-                );
+                let new_cmd = OffsetCommand::new(all_entities);
                 self.command_line.push_info(&new_cmd.prompt());
                 self.tabs[i].active_cmd = Some(Box::new(new_cmd));
             }