feat(text): suppress glyph strokes when SDF text is on

With OCS_TEXT_SDF set, text now renders only as SDF quads: the wire path
skips building glyph-stroke geometry (bins stays empty, so the existing
empty-wire branch still emits the insertion snap point). This removes the
double draw (strokes + SDF) and, as a side effect, fixes the long-standing
snap pollution (#276) — snapping near text no longer catches individual
glyph-stroke endpoints, only the insertion point.

Shared sdf_text_enabled() (cached env read) gates both the collector and
the stroke suppression so they stay in lock-step. Flag off: unchanged.

Verified in-app: TEXT/MTEXT/decorations render clean as single SDF, and
snap no longer hits glyph strokes. Click-pick on text is limited while the
flag is on (no stroke geometry) pending a text OBB pick box.

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

src/scene/text/sdf_atlas.rs

@@ -39,6 +39,14 @@ pub fn text_atlas() -> &'static Mutex<GlyphAtlas> {
     ATLAS.get_or_init(|| Mutex::new(GlyphAtlas::new(1024, 1024)))
 }
 
+/// Whether SDF text rendering is enabled (env `OCS_TEXT_SDF`), read once.
+/// When on, the wire path suppresses text glyph strokes so text draws only as
+/// SDF quads (no double draw); the insertion snap point is kept.
+pub fn sdf_text_enabled() -> bool {
+    static ON: OnceLock<bool> = OnceLock::new();
+    *ON.get_or_init(|| std::env::var_os("OCS_TEXT_SDF").is_some())
+}
+
 // ── Bake configuration ──────────────────────────────────────────────────────
 
 /// Texels per glyph unit. Glyphs live in a 9-unit cap-height space, so a cap