G1: Lift, soft elevation shadows (off by default)

`Lift` (a GUI toggle, capability lift) lifts the focused pane on a
critically damped spring (animation.Spring: closed form, about 240 ms to
settle, velocity kept across retargets, settled = no frames) and floats
notices. The core puts the lift on the regions (Region.lift, on the wire);
the GUI casts from it: a soft shadow is decor, an erf rectangle on one
quad grown by 3 sigma (decor.frag, flag 0x10000000), in the quad's own
space so a track's transform carries it; darken-only, the caster's rect
left alone, alpha pre-warped for linear light and IGN-dithered. Cast last
in its group, so a neighbour's rails and rules darken with its text; a
notice's before its rule. Strength is capped per theme so text over the
darkest shadow keeps min(its contrast, 4.5) (test over the native themes).

Opt-in until the focus lift/dim default is decided. Feel review material:
docs/effects.md. Test-mode PARDES_TEST_SERIES keeps every captured frame.

Shared files touched: pardes.zig (two fields, one nextWake line),
detached/wire.zig (lift on the region), config.zig, builtins.zig
(capability), gui.zig. Not touched: Messages.zig, mouse.zig, tty,
host_io.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/surface.zig b/src/surface.zig
index b6f41853..94b37915 100644
--- a/src/surface.zig
+++ b/src/surface.zig
@@ -364,6 +364,10 @@ pub const Region = struct {
     thumb_h: u16 = 0,
     /// A notice's index in its pane's `notices`.
     notice: u8 = 0,
+    /// How far it stands off the page, 0 to 1: a pane's while it has the
+    /// focus (Lift, on a spring), a notice's while Lift is on. A pixel shell
+    /// casts a soft shadow from it; the tier it is drawn in never changes.
+    lift: f32 = 0,
     /// Cells the column-move rail takes off the right edge while it runs
     /// there: layers and pixel shells stop short of them, the grid does not.
     clip: u16 = 0,