fix(editable-input-rgba): normalize alpha percent and clamp blur to 0–100

[bra3Ik]

When editing HEXA alpha, 10% could revert to 9% after blur due to FP drift and incorrect blur clamping.
This change normalizes rgba.a for display and clamps the alpha input on blur to 0–100, stabilizing 9→10 transitions.

• Normalize alpha percent when rendering
• Add dedicated alpha blur clamp (0–100)

Closes #189
Ref: #189