Save Native and RTG shader parameters

[midwan]

Summary

• add separate Shader Parameters actions beneath the Native and RTG shader selectors
• move Reset to Shader Defaults to the top of each targeted popup and add a Save Parameters action beside it
• persist parameter overrides independently for Native and RTG modes, including when both modes use the same shader
• keep Save Defaults for the remaining Filter defaults: shader selections and bezel settings
• widen the shader-related buttons so their labels remain visible

Root cause

Shader parameter edits only lived in renderer state. The Filter panel's Save Defaults action stored the selected shader names and bezel settings, but it had no serialized parameter state to restore after restarting Amiberry. A single untargeted popup also could not distinguish Native values from RTG values.

User impact

Native and RTG shader parameters can now be edited, reset, saved, and restored independently from their respective controls. Reset followed by Save removes that target's overrides and returns it to the values declared by the shader.

Validation

• built the macOS Debug target successfully after rebasing onto the latest master
• manually verified the revised Filter layout and unclipped button labels
• saved different values for Native and RTG while both selected the same shader, restarted, and confirmed each popup restored its own value
• reset and saved each target independently, confirming only that target's serialized override was removed
• git diff --check