android: port the web studio's HSL selective colour mixer

The rail gains an HSL tab between FX and FRAME, and the tab opens the mixer
ported from the web studio: eight hue bands, each with hue/sat/lum knobs on a
-10..+10 ruler, plus three whole-image moves behind an IMAGE divider. Band
weights are linear tents anchored on HSL_BANDS and summing to 1 at every hue, so
neighbouring bands hand over at exactly half strength and no hue falls in a gap.
Pixels under 8% saturation are gated out of the weights (rgb2hsl calls a neutral
red, so an ungated one would ride the RED band), while the whole-image LUM move
is added after the gate and still lifts a picture that -SAT has pulled to grey.
The mixer runs last in TONE_SKSL, so a band edit is judged on the colour the user
actually sampled.

The eyedropper is library-only: PICK arms a layer over the picture, a tap reads
the rendered pixel off the canvas, points the ruler at the nearest band and
hangs a panel carrying that band's three knobs. A live preview has no pixel to
read, so in camera mode the chip greys out - the mixer itself still runs there,
which is why the camera worklet's tone buffer had to grow from 10 slots to 40: a
missed slot would have pushed NaN into every uniform and taken the whole tone
pass down, not just HSL.

HSL is a LITE feature (the web studio builds it for guests too), and MONOCHROME
switches the mixer off outright - a mono stock has no hue to select. Checked on a
Xiaomi thor against an 8-band chart: +10 whole-image HUE rotates all eight bands
by +30 deg, -10 on one band's SAT flattens that band and leaves the other seven
alone, and a whole-image -SAT drops the camera preview's mean chroma 13.7 -> 0.4
with +LUM still lifting it 116 -> 166. Cut as 1.2.4 / versionCode 6.

RELEASE_NOTES.md

@@ -1,5 +1,23 @@
 # Release notes
 
+## 1.2.4 (versionCode 6)
+
+HSL
+- New HSL tab in the tool rail: the web studio's 8-band selective colour mixer. Each band (RED, ORANGE, YELLOW, GREEN, AQUA, BLUE, PURPLE, MAGENTA) carries hue, saturation and lightness knobs, -10..+10; -10 on SAT is grey, full HUE is a 30 deg turn, full LUM is +0.25.
+- Band weights are linear tents anchored on the 8 hues and summing to 1 at every hue, so neighbouring bands hand over at exactly half strength and no hue falls in a gap. Pixels under 8% saturation are gated out of the weights (rgb2hsl calls them red, and an ungated neutral would ride the RED band), while the whole-image LUM move is added after the gate, so a picture pulled to grey by -SAT still answers +LUM.
+- The mixer runs last in TONE_SKSL, after split-tone/kv and vibrance, so a band edit is judged on the colour the user actually sampled.
+- Library mode gains an eyedropper: PICK arms a layer over the picture, a tap reads the rendered pixel, points the ruler at the nearest band and hangs a panel with that band's three knobs. In camera mode PICK is greyed out - a live preview has no pixel to read - but the mixer still runs in the preview.
+- HUE / SAT / LUM IMAGE move every hue at once, behind an IMAGE divider in the same chip row.
+
+Rail
+- Tool rail order: PRESETS, FAVORITED, WB, LIGHT, FX, HSL, FRAME.
+
+Notes
+- HSL is a LITE feature: both builds get it, no PRO gate.
+- MONOCHROME disables the mixer outright - a mono stock has no hue to select.
+- The camera worklet's tone buffer grew from 10 to 40 slots; a missed slot would have pushed NaN into every uniform and broken the whole tone pass, not just HSL.
+- Measured on a Xiaomi thor against an 8-band chart: +10 whole-image HUE rotates all eight bands by exactly +30 deg, -10 on a band's SAT flattens that band to grey while the other seven stay put, and a whole-image -SAT drops the camera preview's mean chroma from 13.7 to 0.4 with +LUM still lifting it 116 -> 166.
+
 ## 1.2.3 (versionCode 5)
 
 Shutter