Feat: ROADMAP Phase 1-5 batch — trim/extend, plot scale, viewport UX, mline caps, table alignment

- TRIM/EXTEND: Ray and XLine entities supported as cutting boundaries and trim targets;
  trim results in Ray→Line/Ray, XLine→Ray/Ray or Line; hover preview added
- Plot scale override: Fit/1:1/1:2/1:5/1:10/1:20/1:50/1:100/2:1 buttons added to Page Setup
  panel; PageSetupCommit applies scale to PlotSettings
- Viewport UX: locked viewport gets orange border; selected viewport gets white border
- Named view → viewport assignment: Choice dropdown in properties panel copies
  view_target/direction/height to the viewport entity
- MLine caps: perpendicular start/end cap lines added for open (non-closed) MLines
- Wipeout polygon grips: boundary vertices become editable grips when clipping_enabled+Polygonal;
  world→pixel back-projection on drag
- Table cell alignment: CellStyle.alignment (1-9) drives left/center/right + top/middle/bottom
  text positioning; cxf::measure_text() helper added
- New commands/features: DIMCONTINUE (DCO), DIMBASELINE (DBA), TOLERANCE (TOL), TABLE,
  ATTDEF, ATTEDIT, ATTDISP, BREAKATPOINT (BAP), PLOTWINDOW (PW), MLINE (ML);
  DIMSTYLE/DIMCURRENT/CLAYER/LTSCALE/CELTSCALE/SCALETEXT/XDATA/UCSICON/REGEN/DRAWORDER extended
- PLINE arc mode: A/L/CLOSE text input, bulge computation, arc preview
- Warning cleanup: removed unused imports and unreachable patterns

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/scene/cxf.rs

@@ -259,6 +259,29 @@ pub fn tessellate_text_ex(
     out
 }
 
+/// Measure the width of a rendered text string in font glyph units × scale.
+/// Returns the total advance width in world units (height-independent: divide by height for
+/// a normalised ratio, or use directly when `height` is already the desired em size).
+pub fn measure_text(text: &str, height: f32, width_factor: f32, font_name: &str) -> f32 {
+    if text.is_empty() || height <= 0.0 {
+        return 0.0;
+    }
+    let font = get_font(font_name);
+    let scale = height / 9.0;
+    let wf = width_factor.clamp(0.01, 100.0);
+    let mut cursor_x: f32 = 0.0;
+    for ch in text.chars() {
+        if ch == ' ' {
+            cursor_x += font.word_spacing;
+        } else if let Some(glyph) = font.glyph(ch) {
+            cursor_x += glyph.advance + font.letter_spacing;
+        } else {
+            cursor_x += 6.0 + font.letter_spacing;
+        }
+    }
+    cursor_x * scale * wf
+}
+
 // ── Parser ────────────────────────────────────────────────────────────────
 
 fn parse(src: &str) -> CxfFile {