refactor(text): SDF for all text kinds; remove the legacy stroke text path

SDF is the only text renderer now — the stroke path and its LOD ladder are
gone, and the remaining text kinds render as SDF glyph quads too.

- ATTDEF / ATTRIB: carry a GlyphRun so single-line attribute text renders as
  SDF (multi-line already did via layout_mtext). Tolerance / complex-linetype
  text already SDF.
- Remove `sdf_text_enabled()` (the OCS_TEXT_SDF flag / kill switch) and take
  the SDF path unconditionally everywhere: tessellate Text arm (per-group by
  GlyphRun presence), hit_test fallbacks, render gather, complex_lt, table,
  mleader.
- Delete the text LOD ladder: tess.rs baseline/greek block and the
  block_cache greek/baseline path (emit_greeked_text / emit_text_baseline),
  plus the now-dead helpers text_baseline_points / text_greek_obb_tris /
  text_obb_corners_native / mtext_line_count and the LocalWire
  text_height_local / text_obb_local fields. All text is crisp at every zoom;
  text entities are exempt from the sub-pixel stub cull.
- Fix a latent bug: block-internal SDF text was culled because its LocalWire
  aabb_local was [0,0,0,0] (no points) — fold the glyph-quad extent into
  aabb_local and exempt text_verts-carrying wires from the sub-pixel cull.
- Clear the pre-existing dead-code warnings (TextPlacement.elevation, TabKind,
  MTextRunKind::Tab).

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

src/scene/convert/tessellate.rs

@@ -210,8 +210,7 @@ pub fn tessellate(
                 // and text into one Text object (a tolerance frame: box lines =
                 // run-less, cell text = run-groups) keeps the geometry as
                 // strokes and draws only the text as SDF.
-                let sdf_on = crate::scene::text::sdf_atlas::sdf_text_enabled();
-                for group in stroke_groups.iter().filter(|g| !(sdf_on && g.run.is_some())) {
+                for group in stroke_groups.iter().filter(|g| g.run.is_none()) {
                     let lx_v = group.origin[0];
                     let ly_v = group.origin[1];
                     let slx_v = (lx_v - ref_lx_v) * anno + ref_lx_v;
@@ -249,12 +248,12 @@ pub fn tessellate(
                 }
 
                 // ── SDF glyph quads ──────────────────────────────────────
-                // When SDF text is on, build this run's glyph quads here and
-                // carry them on the wire. They ride with the wire through the
-                // tess memo, hit-materialisation and (for block content) the
-                // block-expand transform — no separate document-wide collector.
+                // Build each run's glyph quads here and carry them on the wire.
+                // They ride with the wire through the tess memo, hit-
+                // materialisation and (for block content) the block-expand
+                // transform — no separate document-wide collector.
                 let mut sdf_verts: Vec<crate::scene::pipeline::text_gpu::TextVertex> = Vec::new();
-                if sdf_on {
+                {
                     if let Ok(mut atlas) = crate::scene::text::sdf_atlas::text_atlas().lock() {
                         // Selection tints the whole run; otherwise inline `\C`
                         // colours (bin key) win, falling back to entity colour.
@@ -309,7 +308,7 @@ pub fn tessellate(
                 // guards on `text_verts`). Computed here so both the bins-empty
                 // and the bins-non-empty (tolerance box + text) paths can stamp
                 // it on the SDF text wire.
-                let text_aabb = if sdf_on && !sdf_verts.is_empty() {
+                let text_aabb = if !sdf_verts.is_empty() {
                     let (mut nx, mut ny, mut xx, mut xy) =
                         (f64::MAX, f64::MAX, f64::MIN, f64::MIN);
                     for v in &sdf_verts {
@@ -337,7 +336,7 @@ pub fn tessellate(
                     // the drawing-window (canvas) colour, which masks geometry
                     // behind the text like a wipeout. Box = glyph bounds padded
                     // by (background_scale - 1) × text height.
-                    if sdf_on && text_aabb != WireModel::UNBOUNDED_AABB {
+                    if text_aabb != WireModel::UNBOUNDED_AABB {
                         if let EntityType::MText(m) = entity {
                             let has_fill = m.background_fill_flags & 0x03 != 0;
                             let has_frame = m.background_fill_flags & 0x10 != 0;
@@ -429,8 +428,7 @@ pub fn tessellate(
                     // bounds as a separate outline wire so the text box is
                     // visible for testing. The empty text wire below is left
                     // untouched (still the SDF + pick target).
-                    if sdf_on
-                        && !sdf_verts.is_empty()
+                    if !sdf_verts.is_empty()
                         && crate::scene::text::sdf_atlas::text_box_debug()
                     {
                         let [nx, ny, xx, xy] = text_aabb;