Add per-condition fade effect with editor controls and rendering support

[Player-Doite]

Motivation

• Provide a configurable "fade" visual effect for icons so conditions can reduce an icon's alpha instead of only toggling glow/greyscale.
• Allow per-icon and per-vfx-condition fade strength to be authored in the editor and reused by runtime evaluation.
• Integrate fade handling into existing evaluation and rendering paths without changing existing semantics for glow/greyscale.

Description

• Add fade metadata and alpha to VFX condition entries and return a third value from _EvaluateVfxConditions representing the minimum matched fadeAlpha.
• Propagate fade values through CheckAbilityConditions, CheckItemConditions, CheckAuraConditions, time/logic evaluation loops, EvaluateAll, EvaluateAuras, EvaluateCustom, and other callers so each evaluation now returns fadeAlpha (or nil).
• Apply fade at render time by adding frame._daUseFade and frame._daFadeAlpha, multiplying the base dataTbl.alpha by fadeAlpha when computing frame:SetAlpha(...) and when showing frames.
• Add editor UI controls in DoiteEdit.lua: a Fade checkbox and a small slider (MakeMiniFadeSlider) for ability, aura, and item condition blocks; add fade controls to VFX condition rows, with default fadeAlpha = 0.5 and clamping to [0.1, 1.0].
• Ensure callers that previously expected (show, glow, grey) are updated to accept (show, glow, grey, fadeAlpha) and pass nil where appropriate (custom/Cached error paths).

Testing

• No automated tests were added or run for this change.

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Codex Task