docs: add design doc for heavy blur background replacement

Replace Cloudy with Coil BlurTransformation for unblurred album art issue.

Made-with: Cursor

docs/plans/2026-03-18-heavy-blur-background-design.md

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+# Design: Heavy Blur Background via Coil BlurTransformation
+
+**Date:** 2026-03-18  
+**Status:** Approved
+
+## Problem
+
+The player screen's blurred album art background uses the Cloudy library at its maximum radius of 25. This is insufficient — album art with text remains legible and fine details are still visible, breaking the intended "washed out background" aesthetic.
+
+## Solution
+
+Replace Cloudy with a self-contained Stackblur `BlurTransformation` applied via Coil's image loading pipeline. Blur is baked into the decoded bitmap on a background thread, producing a heavily smeared result with no legible text or sharp edges.
+
+## Changes
+
+### 1. Add `BlurTransformation.kt`
+
+Create `app/src/main/java/xyz/cottongin/radio247/ui/util/BlurTransformation.kt`.
+
+A ~130-line pure Kotlin + Android bitmap Stackblur implementation (no new library dependency). Accepts:
+- `radius: Int` — blur radius (25 is already very aggressive at low scale)
+- `scale: Float` — downsample factor applied before blurring (0.1f = 10% of original size)
+
+### 2. Update `BlurredBackground` in `NowPlayingScreen.kt`
+
+- Remove `.cloudy(radius = 25)` modifier
+- Remove `size(10, 10)` from the `ImageRequest` (scale parameter in the transformation handles downsampling)
+- Add `transformations(BlurTransformation(radius = 25, scale = 0.1f))` to the `ImageRequest`
+- Remove Cloudy import
+
+### 3. Remove Cloudy dependency
+
+- Remove `implementation(libs.cloudy)` from `app/build.gradle.kts`
+- Remove `cloudy` version and library entries from `gradle/libs.versions.toml`
+
+## Parameters
+
+| Parameter | Value | Rationale |
+|-----------|-------|-----------|
+| `radius`  | 25    | Maximum effective Stackblur radius before diminishing returns |
+| `scale`   | 0.1f  | Downsamples to 10% before blurring, destroying fine detail and text |
+
+## Trade-offs
+
+- **No new dependency** — implementation is inlined as a project file
+- **All API levels** — pure bitmap manipulation, no RenderEffect/RenderScript
+- **Background thread** — blur computed by Coil pipeline, zero per-frame GPU cost
+- **Not animatable** — blur is baked at load time; cannot be animated at runtime (acceptable for this use case)