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, 5 insertions, 0 deletions

diff --git a/src/pardes.zig b/src/pardes.zig
index f559b125..449ef798 100644
--- a/src/pardes.zig
+++ b/src/pardes.zig
@@ -4111,6 +4111,10 @@ pub const Pardes = struct {
     theme_file_generation: u32 = 0,
     theme_file_pane: u8 = 0,
     chrome_animation: colors.ChromeAnimation = colors.ChromeAnimation.init(colors.initial_chrome),
+    /// Each pane's lift off the page (Lift): 1 while it has the focus, on a
+    /// spring. `lift_serials` says whose it is, so a reused slot starts flat.
+    lifts: [MAX_PANES]animation.Spring = @splat(.{}),
+    lift_serials: [MAX_PANES]u32 = @splat(0),
     animate_theme_changes: bool = false,
     native_images: bool = false,
     /// The shell can take a changed image a few rows at a time (a texture row
@@ -6213,6 +6217,7 @@ pub const Pardes = struct {
     pub fn nextWake(p: *const Pardes) ?u64 {
         const next = p.stepped_ns + animation.frame_ns;
         if (p.chrome_animation.isActive() or p.presentation.animating()) return next;
+        for (p.lifts) |spring| if (!spring.settled) return next;
         var frames: ?u64 = null;
         if (p.look_hover_wait) |waiting| {
             const delay = config.look_preview_delay_frames orelse return next;