[FEATURE] Blurred album art background effect

[pizza-init]

Feature Request

Add an optional blurred/frosted-glass background using the current album art as the source image.

Requested in: #40

Description:
When album art is displayed, optionally render a blurred, darkened version of it as the full-screen background — similar to the effect seen in Apple Music, Spotify, and other modern players.

Implementation notes:

• LVGL 9 has a built-in blur/recolor filter that could be applied to a stretched copy of the art image
• Could be a toggle in Display Settings (on/off)
• Only active when album art is available; falls back to current solid background color otherwise

[pizza-init]

@johnhenrick3-cpu implemented in v1.6.3-nightly.4126ea6 — please test!

What's in this build:

• Full-screen blurred album art background (replaces the ambient color animation)
• Drop shadow on album art
• Both panels transparent so the blur covers the whole screen seamlessly

How it works (custom implementation, NOT LVGL built-in blur):
LVGL 9.5's built-in blur_radius was evaluated but rejected — it allocates a ~768KB temporary buffer on every dirty redraw which is too expensive on ESP32-P4. Instead we use a lightweight custom approach that runs once per track change in the background art task with zero ongoing overhead:

1. Downsample art 420×420 → 64×64 via box average
2. Apply 5-pass box blur on the 64×64 buffer (approximates Gaussian blur)
3. Bilinear upscale to 800×480

Total cost ~185K ops (<1ms), runs in background, never touches the UI thread.

Let us know if you like it or want it as an optional toggle in Display Settings!

[johnhenrick3-cpu]

Looks good so far

one small issue if the next album has no album art blurred background of previous one remains not sure whether you can clear this ?

John

[johnhenrick3-cpu]

all working well

one small issue if the next track has no album art blurred background and music note is shown blur of previous one remains not sure whether you can clear this ?