[raiseCatError]

Stacked on #519 (Slice 4), so this diff is Slice 5 only. Retarget only after review.

What

• Previews in the shared Shader Studio (Kitty and Ghostty):
  • A small sample terminal, drawn by NMSh in cells, shows an approximation of the selected preset. It is labelled "approximate, drawn by NMSh; 's GPU shader is the real effect".
  • A run plays once on selection or a value change, and P replays it. The shared presentation clock runs only while a run animates; there is no idle loop.
  • Reduced Motion and Effects Off show a still frame. NO_COLOR shows no preview.
  • Colors follow the terminal's color level.
  • Short or very narrow windows drop the preview rather than cutting the list or controls.
  • Kitty sliders map onto the preview, so moving one changes it.
  • Effects with no faithful approximation say so instead of guessing.
• Kitty catalog completed: CRT (blue), Rockets, Bloom, TFT pixels, Water, Underwater, Negative.
  • Parameters appear only where Kitty's shipped shaders declare them.
  • CRT and CRT (blue) are mutually exclusive.

Verification

• Focused tests: 121/121. Typecheck clean.
• Installed Kitty 0.49.2, headless with a private HOME: every new preset compiles, and tuned values change the compiled shader compared with the defaults.
• Independent review found no blocker. Its 4 should-fix items and the minor items were fixed with regression tests.
• The full suite is left to CI.

Not verified: GPU output and physical QA were not run.