Motion flavours differ by design, and drive notice drops and pane moves

The flavours looked alike because Lift, the only motion that read them,
moves a shadow a few pixels: overshoot and wind-up were sub-pixel. By design
now: crisp leaves at full speed and never passes its mark; smooth (the
default) eases in and out in twice crisp's time, a slide arriving in 208 ms
(inside §8.1's 220); bouncy passes its mark by ~30% and settles twice;
playful winds up, passes by ~40%, and stretches and squashes, text included
(the user's choice). Small motions are exaggerated by the flavour's gain.

Motion gains launch, gain, span and norm, and ease(u)/speed(u) for moves of
fixed length. The notice drop follows ease() over its fall (alpha never
behind its position) and stays inside its pane's body past its row. Panel
tracks carry the flavour in Track.motion (the old padding byte; macOS header
name follows); opening and moving slides, zooms and rises follow it over
span x their frames; landed, a pane is exactly its target; closing keeps
its own exit. A pane past its mark never takes a neighbour's click; a
rising one stays in its box.

Tests: each flavour's lift trajectory distinct; flavour character; exact
landing bit for bit; a stretched pane's drawn cells map back; the overshoot
hit rule; the vertical clip at peak; legacy tests pinned to crisp. GUI
golden 18-mid-transition changes (the retuned smooth slide at frame 6).

Shared files: src/animation.zig, src/Presentation.zig, src/Messages.zig,
src/macos.zig, src/config.zig, src/pardes.zig tests, src/ninep/screen.zig
test, docs/effects.md, docs/config.md.

2 files changed, 28 insertions, 11 deletions

diff --git a/docs/config.md b/docs/config.md
index 324b54e9..921f817e 100644
--- a/docs/config.md
+++ b/docs/config.md
@@ -537,7 +537,7 @@ Lift rim         a hairline just above the focused tag (light, or shade on a lig
 Lift auto        a shadow on a light page; on a dark one the others recede
 Lift off
 InactiveDim 30   the unfocused panes' text fades 30% toward its ground
-Motion smooth    off, crisp, smooth, bouncy or playful
+Motion smooth    off, crisp, smooth (the default), bouncy or playful
 GripWidth 150    the grip's button and the scrollbar under it, percent of the
                  theme's rail_px (12px at a 17px tagline; 50 to 300)
 ```
diff --git a/docs/effects.md b/docs/effects.md
index eefa52d3..3f375b7d 100644
--- a/docs/effects.md
+++ b/docs/effects.md
@@ -26,18 +26,31 @@ why. The verdict is the user's.
 
 ## Motion flavours
 
-`Motion off|crisp|smooth|bouncy|playful` (default smooth) is one parameter set
+`Motion off|crisp|smooth|bouncy|playful` (default smooth, tuned so arrivals
+land inside §8.1's 220 ms; bouncy and playful run longer, opt-in) is one parameter set
 (animation.Motion) every fx animation reads, so a flavour is data, not a
 branch in each effect. Input is never blocked, and a new target always
 retargets from the current position and velocity.
 
-| flavour | timing (ω) | follow-through (ζ) | anticipation | squash/stretch | secondary lag | arcs |
-|---|---|---|---|---|---|---|
-| off | instant | — | — | — | — | — |
-| crisp | 44 | 1 (none) | — | — | in step | — |
-| smooth | 26 | 1 (none) | — | — | 0.85 | 0.04 |
-| bouncy | 30 | 0.55 (overshoots ~12%) | — | 0.12 | 0.8 | 0.08 |
-| playful | 24 | 0.42 (overshoots ~23%) | 0.08 of the move | 0.25 | 0.7 | 0.15 |
+| flavour | timing (ω, length) | follow-through (ζ) | anticipation | squash/stretch | exaggeration (gain) | secondary lag | arcs |
+|---|---|---|---|---|---|---|---|
+| off | instant | — | — | — | — | — | — |
+| crisp | 60, 0.6× (leaves at full speed) | 1 (none) | — | — | 1 | in step | — |
+| smooth | 34, 1.1× (slow in, slow out; ≤220 ms) | 1 (none) | — | — | 1 | 0.85 | 0.04 |
+| bouncy | 24, 1.4× | 0.35 (overshoots ~30%, settles twice) | — | 0.15 | 1.25 | 0.8 | 0.08 |
+| playful | 18, 1.7× | 0.28 (overshoots ~40%) | 0.15 of the move | 0.35 | 1.4 | 0.55 | 0.15 |
+
+The flavours are distinct by design, not tuning: crisp leaves at full speed
+and never passes its mark; smooth takes twice as long and eases in and out; bouncy clearly passes its mark and settles back once or twice;
+playful winds up the other way first, flies well past, and stretches along
+its path and squashes as it lands, its text with it (the user's choice); a
+pointer inverts the same stretched box, and landed, a pane is exactly its
+target. A motion only a few pixels big (Lift) is
+exaggerated by the flavour's gain so its character shows. The flavours drive
+the Lift spring (time-based), the notice drop and the pane moves (PanelSlide,
+PanelZoom, PanelVertical opening or moving, whose length scales with the
+flavour); a closing pane keeps its effect's own exit. Chart and side-by-side
+video: .scratch/render/motion/compare/.
 
 Which principles each motion uses:
 
@@ -45,8 +58,12 @@ Which principles each motion uses:
   (bouncy and playful lift past full and settle back), anticipation (playful
   dips before it rises; below zero nothing is drawn, so it reads as a beat
   before the lift), staging (only the focused pane lifts; nothing else moves
-  with a focus change). Squash, stretch, arcs and secondary lag have nothing
-  to act on in a lift.
+  with a focus change), exaggeration (the flavour's gain). Squash, stretch,
+  arcs and secondary lag have nothing to act on in a lift.
+- **Notice drop and pane moves**: timing and follow-through from the flavour's
+  spring over the move's length; anticipation (playful). A pane past its mark
+  never takes a neighbour's click, a rising one stays in its box, and a notice
+  past its row stays in its pane's body.
 - **Cursor** (G3, next): designed around the same set: glide on the spring,
   stretch along the path, an arc on long jumps, the trailing corners as the
   secondary action.