fix(tui): stop drawing from the unicode blocks a plain terminal font lacks

Three separate "why are there boxes" reports, and I fixed them one glyph at a
time instead of as a class, so the next one was always waiting. Grouping the
tester's terminal by unicode block made the rule obvious:

  RENDERS   Latin-1 (·), Box Drawing (─ │), Block Elements (█ ▛ ▐),
            Geometric Shapes (○ ▶), General Punctuation (…), Arrows
  TOFU      Miscellaneous Technical (⏎ U+23CE, ⏵ U+23F5), the sparse end
            of Dingbats (❯ U+276F)

That is an ordinary font, not a broken one, so it is the profile to design
against. The working spinner moves off Dingbats and Math Operators onto
quadrant blocks (▖▘▝▗) — the same block as the `▛█▐` art claude itself draws,
which that font renders fine — and the blocked marker moves off `⚠`
(Misc Symbols, emoji presentation on many terminals) onto `▲`, the block that
already gives us `▶` and `○`.

The preview fold gains claude's own spinner dingbats (✢ ✳ ∗ ✻ ✽ ✴ → `*`) and
`⚠` → `!`. Its animated status line is exactly where a reader looks, so tofu
there is the most visible kind there is.

A test now enforces this as a CLASS: no glyph in the unicode set may come from
Misc Technical, Misc Symbols or Dingbats, with U+2714 the single documented
exception because it was observed rendering on the very font that failed the
others. Verified by scanning a live frame driven with the tester's exact
environment: zero glyphs from any of the three blocks.

src/tui/tui-ansi.ts

@@ -354,6 +354,16 @@ const PREVIEW_GLYPH_FOLD: ReadonlyMap<string, string> = new Map([
   ['\u23F7', 'v'], // ⏷
   ['\u2771', '>'], // ❱
   ['\u2770', '<'], // ❰
+  // claude's own working/done spinner cycles through these, and they are the
+  // same sparse-Dingbats class as `❯`: the animated line is exactly where a
+  // reader looks, so tofu there is the most visible kind.
+  ['\u2722', '*'], // ✢
+  ['\u2733', '*'], // ✳
+  ['\u2217', '*'], // ∗
+  ['\u273B', '*'], // ✻
+  ['\u273D', '*'], // ✽
+  ['\u2734', '*'], // ✴
+  ['\u26A0', '!'], // ⚠ Misc Symbols, and emoji-presentation on many terminals
 ]);
 
 /**