feat: add cue color and brightness settings for annotation text

[nathanael]

Summary

• Adds Cue Color and Cue Brightness settings in the Appearance tab for customizing teleprompter annotation cues (e.g. [pause], [smile], [breath]).
• Previously annotations were hardcoded to white at fixed opacities.
• Cue Color: 6 color presets (same as highlight color options)
• Cue Brightness: 4 levels (Dim, Low, Medium, Bright) controlling opacity
• Settings preview includes a [pause] sample so users can see the effect live
• Remote viewer (BrowserServer) and DirectorServer updated for consistency

Test plan

• Open Settings > Appearance -- Cue Color and Cue Brightness controls should appear below Highlight Color
• Change Cue Color -- [pause] in the preview should change color
• Change Cue Brightness -- [pause] opacity should visibly change across all 4 levels
• Add text with [breath] or [smile] annotations, press play -- annotations should use the configured cue color and brightness
• Enable Remote Connection, open browser viewer -- annotations should render with cue color

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