Add ticker text design doc

Captures the design for replacing BounceMarqueeText with a
constant-speed TickerText composable (33 dp/s, continuous leftward
scroll with gap looping).

Made-with: Cursor

docs/plans/2026-03-11-ticker-text-design.md

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+# Ticker Text Design
+
+## Problem
+
+The `BounceMarqueeText` composable in `NowPlayingScreen.kt` scrolls long text at a speed proportional to overflow, clamped to 2000–8000ms. For very long titles, the 8000ms cap means the text covers more distance in the same time — making it visibly faster and harder to read. The bounce-back pattern (scroll left, pause, scroll right) also feels unnatural compared to a continuous ticker.
+
+## Decision
+
+Replace `BounceMarqueeText` with a `TickerText` composable that scrolls at a constant 33 dp/s leftward, regardless of text length.
+
+## Design
+
+### `TickerText` composable
+
+**Parameters:**
+- `text`, `style`, `color`, `strokeColor`, `strokeWidth`, `modifier` — same as current `BounceMarqueeText`
+- `velocityDpPerSecond: Float = 33f` — constant scroll speed
+
+**Behavior:**
+- Text fits in container: rendered centered and static (no animation).
+- Text overflows: scrolls continuously leftward at 33 dp/s.
+- After the text exits the left edge, a gap equal to the container width passes (screen appears empty), then the text reappears from the start position and repeats.
+
+**Animation math:**
+- `totalScrollPx = textWidthPx + containerWidthPx`
+- `durationMs = (totalScrollPx / (velocityDpPerSecond * density)) * 1000`
+- No upper clamp — longer text simply takes longer at the same speed.
+- Keyframes: `0f` → `-(textWidthPx)` with `LinearEasing`, then restart.
+- Initial delay of ~1.5s before first scroll so user can read the beginning.
+
+**Stroke overlay:** Both the stroke `Text` and fill `Text` remain in the same translated `Box`, moving together.
+
+**Callers:** `TrackInfoSection` swaps `BounceMarqueeText` → `TickerText` with no other changes.
+
+## Rejected alternatives
+
+- **`Modifier.basicMarquee()`** — less control over gap/looping, uncertain Compose BOM version support, harder to keep the stroke overlay working.
+- **Custom `Canvas` + `drawText`** — maximum control but overkill; significantly more code for the same result.