refactor(text): per-entity SDF text — all text kinds, selection/hover highlight

Rearchitect SDF text from a document-wide collector to per-entity
production during tessellation, so each entity owns its glyph quads and
composite/nested text is covered for free (no re-explosion, no per-frame
document walk).

- WireModel gains `text_verts`: glyph quads ride on the wire, so they are
  cached by the tess memo, cloned on hit, and transformed by the block
  expand loop exactly like `points`.
- Text arm (tessellate.rs) builds the quads when SDF is on and suppresses
  the strokes; render gathers text_verts from the viewport wire set
  (`gather_text_verts`, cached on wire content id) — the old collector is
  removed. Covers model, dimension, table, block-internal and paper-sheet
  text uniformly.
- MLEADER text (lays out via layout_mtext, not the Text arm) gets its own
  SDF branch driven by the per-run GlyphRun.
- Pick box comes from the rendered glyph quads (true text extent), not
  entity_aabb which mis-places the box for MTEXT; composite paths no longer
  clobber the empty text wire's tight AABB (dim pick box hugs the text).
- Selection / hover highlight via a text-highlight overlay (upload_text_
  highlight, keyed on selection_generation) mirroring the selected-wire
  xray overlay; base glyphs stay neutral so a deselect leaves no stale tint.
- Debug: env OCS_TEXT_BOX draws each run's glyph-bounds rectangle.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/app/update/viewport.rs

@@ -1166,6 +1166,7 @@ pub(super) fn on_tick(&mut self, t: Instant) -> Task<Message> {
                                 let far_pos = base + dir * far;
                                 let far_neg = base - dir * far;
                                 let guide = crate::scene::WireModel {
+            text_verts: Vec::new(),
                                     name: "__polar_guide__".into(),
                                     points: vec![
                                         [far_neg.x, far_neg.y, far_neg.z],
@@ -1199,6 +1200,7 @@ pub(super) fn on_tick(&mut self, t: Instant) -> Task<Message> {
                             let far_pos = h.base + h.dir * far;
                             let far_neg = h.base - h.dir * far;
                             previews.push(crate::scene::WireModel {
+            text_verts: Vec::new(),
                                 name: "__otrack_guide__".into(),
                                 points: vec![
                                     [far_neg.x, far_neg.y, far_neg.z],