fix(scene): per-line text greek honors word-wrap subline count

`text_obb_corners_native` derived MText line count from explicit `\n`
matches in `m.value`, so any MText that relied on `\P`/`\N` breaks or
word-wrap (rectangle_width-driven) reported a single line. The greek
emitter then split the OBB into one row and the user saw a single box
on top of a 5-line wrapped paragraph.

  - text_support: new `mtext_line_count` — strip codes, split on
    \n/\P/\N, word-wrap each paragraph against `rectangle_width`,
    sum. Same line splitting the MText/MultiLeader renderers already
    perform; centralized for reuse.
  - text_obb_corners_native: takes `mtext_lines_override: Option<usize>`.
    When supplied, OBB height = h_world × n × line_spacing_factor; this
    also overrides a possibly stale `rectangle_height` on resaved DWGs.
  - Top-level greek paths (scene/mod.rs) compute the line count via
    `mtext_line_count` and pass it through to baseline / rect emission.
  - block_cache: tessellate_sub_local computes the count at defn build
    so the stored `text_obb_local` is wrap-aware; emit_text_baseline
    and emit_greeked_text recover n_lines from `ulen / h_local` as
    before and now produce the correct per-row split inside Inserts.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/entities/text_support.rs

@@ -341,6 +341,35 @@ pub fn measure_mtext_chars(text: &str, scale: f32, font: &cxf::CxfFile) -> f32 {
     width
 }
 
+/// Total number of visible lines an MText renders to — explicit `\P` /
+/// `\n` / `\N` breaks plus word-wrap induced sublines when
+/// `rectangle_width > 0`. Mirrors the line-splitting `entities/mtext.rs`
+/// and `tessellate_multileader` perform; lets renderers split the OBB
+/// into per-row LOD primitives without re-running the wrap measurement.
+pub fn mtext_line_count(
+    m: &acadrust::entities::MText,
+    document: &CadDocument,
+    anno_scale: f32,
+) -> usize {
+    let resolved = resolve_text_style(&m.style, document);
+    let font = cxf::get_font(&resolved.font_name);
+    let width_factor = resolved.width_factor.max(0.01);
+    let height = m.height as f32 * anno_scale;
+    let plain = strip_mtext_codes(&m.value);
+    let explicit = split_mtext_lines(&plain);
+    let total: usize = if m.rectangle_width > 0.0 && height > 0.0 {
+        let scale = height / 9.0 * width_factor;
+        let max_w = m.rectangle_width as f32 * anno_scale;
+        explicit
+            .iter()
+            .map(|l| word_wrap(l, max_w, scale, font).len())
+            .sum()
+    } else {
+        explicit.len()
+    };
+    total.max(1)
+}
+
 pub fn word_wrap(text: &str, max_w: f32, scale: f32, font: &'static cxf::CxfFile) -> Vec<String> {
     if max_w <= 0.0 || text.is_empty() {
         return vec![text.to_string()];