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/text/sdf_atlas.rs

@@ -39,18 +39,9 @@ pub fn text_atlas() -> &'static Mutex<GlyphAtlas> {
     ATLAS.get_or_init(|| Mutex::new(GlyphAtlas::new(1024, 1024)))
 }
 
-/// Whether SDF text rendering is enabled, read once. Default ON — text draws
-/// as SDF glyph quads (crisp at every zoom, no LOD; the wire path suppresses
-/// the glyph strokes and keeps the insertion snap). Set `OCS_TEXT_SDF=0` to
-/// fall back to the legacy stroke path (kill switch for the stroke renderer).
-pub fn sdf_text_enabled() -> bool {
-    static ON: OnceLock<bool> = OnceLock::new();
-    *ON.get_or_init(|| std::env::var("OCS_TEXT_SDF").map_or(true, |v| v != "0"))
-}
-
 /// Debug: when env `OCS_TEXT_BOX` is set, each SDF text run also emits a
 /// rectangle outline around its glyph bounds so the text pick box is visible.
-/// Read once. Only meaningful together with [`sdf_text_enabled`].
+/// Read once.
 pub fn text_box_debug() -> bool {
     static ON: OnceLock<bool> = OnceLock::new();
     *ON.get_or_init(|| std::env::var_os("OCS_TEXT_BOX").is_some())