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, 16 insertions, 0 deletions

diff --git a/src/draw.zig b/src/draw.zig
index 2d757635..0998db24 100644
--- a/src/draw.zig
+++ b/src/draw.zig
@@ -119,6 +119,22 @@ pub fn place(p: *Pardes, s: *Surface) void {
         s.addRegion(.{ .kind = .workspace_tag, .rect = .{ .x = 0, .y = 0, .w = s.cols, .h = p.topBarHeight() } });
     // A column carried to the window's right edge shows where it lands as a
     // rail in the last cell: the layers under it stop a cell short.
+    // Lift: the focused pane rises, the others settle back, each on its
+    // spring; a notice floats while Lift is on.
+    for (&p.panes, &p.lifts, &p.lift_serials, 0..) |slot, *spring, *serial, id| {
+        const pane = slot orelse continue;
+        if (serial.* != pane.serial) {
+            serial.* = pane.serial;
+            spring.* = .{};
+        }
+        spring.retarget(if (p.settings.lift and id == p.active) 1 else 0, p.stepped_ns);
+        _ = spring.step(p.stepped_ns);
+    }
+    for (s.regions[0..s.nregions]) |*region| switch (region.kind) {
+        .grip, .tag, .body, .rail => region.lift = p.lifts[region.owner].value(p.stepped_ns),
+        .notice => region.lift = if (p.settings.lift) 1 else 0,
+        else => {},
+    };
     if (p.drag == .column_move) rail: {
         const d = p.drag.column_move;
         const source = layout.columnBySerial(p, d.serial) orelse break :rail;