fix(perry-ui-ios): #1107 partial-alpha text invisible on iOS 26

[proggeramlug]

Closes #1107.

Root cause

On iOS 26 device, UILabel.setTextColor: and UIButton.setTitleColor:forState: with a UIColor whose alpha < 1.0 render zero glyphs. Reporter confirmed:

• alpha == 1.0 paints fine (same code path)
• iOS 17 simulator is unaffected (only iOS 26 device fails)
• AttributedText widget's path — UIColor under NSColor / NSForegroundColorAttributeName inside an NSAttributedString applied via setAttributedText: — renders correctly with sub-1.0 alpha

Looks like an iOS 26 / Liquid Glass text renderer regression: the plain textColor / titleColor paths are silently dropped (or rasterised invisibly) when the color isn't fully opaque, while the attributed-text path goes through a different renderer that still honors partial alpha.

Fix

In crates/perry-ui-ios/src/widgets/text.rs::set_color (UILabel) and crates/perry-ui-ios/src/widgets/button.rs::set_text_color (UIButton): for alpha < 1.0, mirror AttributedText::append's known-working code path on the plain widget by also setting attributedText / attributedTitle:forState::

1. Read the current text / titleForState:UIControlStateNormal
2. Read the current font (from the label or button.titleLabel.font)
3. Build an NSAttributedString with NSFont + NSColor attrs (matching attributed_text.rs line-for-line on the keys)
4. Apply via setAttributedText: / setAttributedTitle:forState:UIControlStateNormal

setTextColor: / setTitleColor: is still issued first, so any later setText: / setTitle: clobber (which discards the attributed buffer) retains a reasonable solid-color fallback. For alpha == 1.0 we explicitly clear any prior attributedText/attributedTitle so the plain path takes over, avoiding disturbing intrinsic-content sizing on the unaffected iOS 17 path.

Critically, the NSFont attr is always emitted — the reporter's "Routing set_color through setAttributedText: with NSColor in attributes dict … Zero-glyph" bisection-step likely didn't include NSFont, and on iOS 26 it appears NSFont is required for sub-1.0 alpha to render.

Files touched

• crates/perry-ui-ios/src/widgets/text.rs
• crates/perry-ui-ios/src/widgets/button.rs

No TS / HIR / codegen / shim changes.

Test plan

The agent doesn't have iOS 26.5 device access. Reporter should validate:

• On iOS 26.5 device, run the issue reproducer:

  import { Text, VStack, textSetFontSize, textSetColor } from "perry/ui";
  const TEXT_PRIMARY = { r: 0, g: 0, b: 0, a: 0.87 };
  const slogan = Text("Erlebe eine Welt, in der Teilen Freude schenkt");
  textSetFontSize(slogan, 24);
  textSetColor(slogan, TEXT_PRIMARY.r, TEXT_PRIMARY.g, TEXT_PRIMARY.b, TEXT_PRIMARY.a);

  expect: 87%-black glyphs visible.
• Same on a Button(...) title with textSetColor(btn, 0, 0, 0, 0.87) — expect 87%-black glyphs.
• iOS 17 simulator regression check: Text + textSetColor with both alpha == 1.0 and alpha == 0.87 still render.
• Existing AttributedText widget still works (untouched code path; smoke test only).

If the alpha < 1.0 cases still come out blank on device, the next hypothesis is that NSColor (the iOS legacy key) needs to be NSForegroundColorAttributeName literal (@"NSColor" resolves to the same symbol but if Apple changed it on iOS 26, we'd want to look up kCTForegroundColorAttributeName from CoreText instead). Easy follow-up if validation fails.

No version bump or changelog change — maintainer will fold those in at merge.