Implement the measure boxes on the operations - #54

Summary

Typed dimensions are now shown in floating boxes placed on the edge they affect (similar to Fusion 360), instead of only in the status-bar field.

• Line, circle, polygon, arc chord, move: the box sits on the midpoint of the segment being measured and shows the live value, or the typed text with a caret.
• Rectangle / image: separate Width and Height boxes on adjacent sides. Tab / Shift+Tab switches fields and selects the value, so typing replaces it. Either side can be left empty to keep the size under the cursor.
  The 5m,50mm syntax still works.
• Arc height: the box sits on the sagitta (chord midpoint → apex) and shows the actual arc height.
• Push/Pull: shows the distance; the resulting total depth appears as a second line only for already extruded faces (previously "Difference" and "Total" repeated the same value on fresh faces, and the text was not translated).
• Freehand, offset, rotate, scale: box next to the cursor.
• Invalid input turns the box border red.
• Spaces in dimensions: 2 cm now works like 2cm. While a dimension is being typed, Space and letter keys no longer trigger tool shortcuts. With an empty dimension, Space still switches to Select.

The status-bar field is hidden while floating boxes are enabled. It is still used when the new View → Floating Dimension Input option is turned off (persisted, on by default), and for Tape Measure and Protractor.

Implementation notes

• New module crates/benchup-app/src/dimension_overlay.rs. The boxes are display-only: typed text already flows into length_input without focus, so a second focusable text field would duplicate input.
• Rectangle input keeps the existing width,height buffer format, so formulas, the status-bar field and commit logic are unchanged.
• New translation keys in all catalogs: app.width, app.height, app.push_pull_total, sidebar.floating_dimension_input; updated rectangle hint text.

Tests

Added coverage for Tab/Shift+Tab field switching and selection, single-side rectangle input, invalid sides, input length limit, arc height (sagitta), Push/Pull total, spaces inside dimensions, the hidden status-bar field, and persistence
of the new option.