fix(text): show text in command previews (move/copy/etc) (#316)

Command previews (MOVE, COPY, ROTATE, SCALE, STRETCH, MIRROR, ARRAY,
PASTE, INSERT) build ghost WireModels via WireModel::translated/rotated/
scaled/stretched/mirrored, but those helpers moved only `points`, never
`text_verts`, and the ghosts' glyphs were never uploaded — so text
vanished (or froze at its source) during the preview, same root cause as
the grip-drag case.

Transform text_verts alongside points in all five helpers (shared
map_text_verts, reconstructing + re-splitting the double-single world
position), and gather preview_wires' glyphs into the per-frame
preview-text buffer in the render path. This covers every command
preview automatically. The grip-drag else branch no longer sets
preview_text explicitly (the render gather handles it); the grip-slide
fast path keeps its own scene.preview_text channel (empty preview_wires,
so no double-draw).

MIRROR honours MIRRTEXT: on -> true glyph mirror via mirrored(); off ->
readable relocation via translated().

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

src/scene/pipeline/text_gpu.rs

@@ -70,7 +70,7 @@ impl TextVertex {
 
 /// Split an f64 into the double-single (high f32, low residual f32) pair the
 /// shaders reconstruct relative-to-eye.
-fn split_ds(v: f64) -> (f32, f32) {
+pub(crate) fn split_ds(v: f64) -> (f32, f32) {
     let high = v as f32;
     (high, (v - high as f64) as f32)
 }