F13 follow-up — Improve CRT visual fidelity

[Flow-Fly]

Follow-up to #124 after the initial CRT feature shipped through PRs #296 and #299.

Status

Deferred. The current CRT feature is accepted and should remain available as-is. This issue is not part of the active agent queue.

Goal

Improve the visual fidelity of the CRT effect so pixel art gains more of the depth, color blending, and apparent detail associated with real CRT displays.

Candidate improvements

• tune RGB phosphor geometry and mask scaling across preview sizes and exports
• improve horizontal beam spread, scanline shape, bloom, and channel bleed
• compare aperture-grille, arcade-monitor, and consumer-TV profiles against real CRT references
• make profile differences clearer without sacrificing legibility or performance
• add repeatable visual comparison fixtures or screenshot proof

Constraints

• remain display-only and non-destructive
• keep clean exports unchanged
• reuse the generic view-effect pipeline
• require human visual acceptance before merge

Exit criteria

A future implementation should include side-by-side reference comparisons at representative sprite sizes and a manual playtest confirming that the profiles add depth without obscuring the original pixel art.