PCIOS-805: Fix transcript controls layout shift causing mis-taps

[pocketcasts]

Resolves https://linear.app/a8c/issue/PCIOS-805/ios-transcript-controls-shift-position-as-the-transcript-loads-causing

Summary

Fixes a layout shift in the transcript controls bar where buttons would reposition as the transcript loaded, causing taps intended for Share to land on Play.

Changes

• Always add shareButton and playButton to the stack view upfront (instead of conditionally via if guards), using .isHidden for static feature flag / context gating
• Replace searchButton.isHidden toggling in loading/loaded states with alpha + isUserInteractionEnabled toggling — this keeps the button in the UIStackView layout (preserving its space) so the flexible spacer does not expand/contract and shift the other buttons
• Apply the same alpha-based visibility to all control buttons (share, play, search) during the loading transition so they all appear together

Verification

• Lint: PASS
• Tests: N/A — pre-existing CarPlay build errors unrelated to this change
• Diff review: PASS — single file changed, minimal diff, no unintended changes
• Secret scan: PASS

Confidence

HIGH — The root cause is clearly identified and the fix uses standard UIKit patterns.

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This PR was created autonomously by linear-solver.
Triage complexity: simple | Linear issue

[Copilot]

Pull request overview

This PR addresses a UIKit UIStackView layout shift in TranscriptViewController’s transcript controls bar that could cause mis-taps while the transcript is loading (buttons changing position as subviews are added/removed or hidden/unhidden).

Changes:

• Always add shareButton and playButton as arranged subviews up front, gating them via .isHidden instead of conditional insertion.
• Keep control button layout stable during loading by switching from isHidden toggling to alpha + isUserInteractionEnabled toggling.
• Apply the same visibility approach to all relevant control buttons so they appear/disappear together during the loading transition.