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/scene/text/complex_lt.rs

@@ -208,6 +208,7 @@ pub fn apply_along(
         .into_iter()
         .filter(|s| s.len() >= 2)
         .map(|pts| WireModel {
+            text_verts: Vec::new(),
             name: name.to_string(),
             points: pts,
             points_low: Vec::new(),

src/scene/text/sdf_atlas.rs

@@ -47,6 +47,14 @@ pub fn sdf_text_enabled() -> bool {
     *ON.get_or_init(|| std::env::var_os("OCS_TEXT_SDF").is_some())
 }
 
+/// 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`].
+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())
+}
+
 // ── Bake configuration ──────────────────────────────────────────────────────
 
 /// Texels per glyph unit. Glyphs live in a 9-unit cap-height space, so a cap