feat(text): parse TEXT via acadrust + extend SDF text to MTEXT

Two related steps for the text pipeline:

- TEXT parsing now goes through acadrust's parse_plain_text (like MTEXT
  uses parse_mtext). text::acad_text_encode parses the value's %% codes —
  including %%u/%%o underline/overline and %%nnn — and re-encodes to the
  stroke tessellator's \L/\O + resolved-Unicode grammar, so OCS no longer
  tokenizes TEXT %% codes itself. (ATTRIB/TOLERANCE/DIMENSION still use the
  local tokenizer for now.) Bumps the acadrust pin to the commit that
  completes the TEXT/MTEXT control-code set.

- SDF text (OCS_TEXT_SDF) now covers MTEXT and every text-producing
  entity, not just top-level TEXT. TextStroke carries a GlyphRun (layout
  params); the collector walks convert()'s TruckObject::Text runs and
  applies annotation scale exactly as tessellate does for strokes.
  layout_glyph_quads shares lff::tokenize_run so %% specials resolve and
  \L/\O decorations are skipped (decoration LINES in SDF are still TODO).

Verified: stroke rendering unchanged with the flag off; SDF glyphs render
correctly for TEXT and MTEXT with OCS_TEXT_SDF=1. 154 lib tests green.

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

src/scene/text/glyph_quads.rs

@@ -70,11 +70,22 @@ pub fn layout_glyph_quads(
     let mut cursor_x = 0.0f32;
     let mut quads = Vec::new();
 
-    for ch in text.chars() {
-        if ch == ' ' {
-            cursor_x += face.word_spacing();
-            continue;
-        }
+    // Same token walk as `tessellate_text_run` (LFF branch): DXF `%%` specials
+    // resolve to glyphs, spaces/missing advance the pen, decoration toggles emit
+    // no glyph (they render as lines on the stroke path).
+    for tok in crate::scene::text::lff::tokenize_run(text) {
+        let ch = match tok {
+            crate::scene::text::lff::Tok::Glyph(c) => c,
+            crate::scene::text::lff::Tok::Space => {
+                cursor_x += face.word_spacing();
+                continue;
+            }
+            crate::scene::text::lff::Tok::Missing => {
+                cursor_x += 6.0 + face.letter_spacing() * tracking;
+                continue;
+            }
+            crate::scene::text::lff::Tok::Deco(..) => continue,
+        };
         match atlas.get_or_insert(font_name, ch) {
             Some(e) => {
                 let (lo, hi) = (e.plane_min, e.plane_max);
@@ -91,8 +102,7 @@ pub fn layout_glyph_quads(
                 cursor_x += e.advance + face.letter_spacing() * tracking;
             }
             None => {
-                // No ink (whitespace glyph) or atlas full: advance only, using
-                // the glyph's own advance when the font knows it.
+                // No ink (whitespace glyph) or atlas full: advance only.
                 let adv = face.glyph(ch).map(|g| g.advance).unwrap_or(6.0);
                 cursor_x += adv + face.letter_spacing() * tracking;
             }