G3: the focused cursor glides a jump on the Motion flavour's springs, and blinks

The core owns the motion, as Lift: animation.CursorGlide keeps the focused
cursor's four corners on springs (leading corners at the flavour's pace x2.4,
trailing ones x follow, so a jump smears and collapses; a long jump bows by
the flavour's arc), sampled at each frame's own time. A step of a cell or
less, insert mode, a focus change and any scroll (a file's view, a
terminal's output) land at once; a snap lands a glide under way too. The
quad is clamped to the focused pane when drawn (never its springs). Chrome
carries it on the wire (cursor_glide: bit 1 a cursor, bit 0 gliding;
cursor_alpha; cursor_quad, grid cells; cursor_idle_ms): the GUI draws the
quad as an overlay in the cursor's colour, at 85% (70% on the long
flavours) rising to solid as it lands, and hides the cells' cursors while it
does: one or the other every frame. Only the focused cursor glides.

Blink (CursorBlink, on by default in pixel shells) is the shell's: from
cursor_idle_ms and when the frame arrived, solid while typing and 500 ms
after, 530 ms halves with 80 ms eased edges, solid after 10 s idle, and
never while the window is unfocused or minimized or on a virtual clock. An
edge redraws the last frame with no core render (level B, blink_redraws);
an attached GUI blinks from the same field without a frame per edge.

Tests: snaps a cell, glides a jump with smear and bow, arrives under a pixel
by 150 ms on smooth and lands exactly, shifts with a scroll; blink holds,
eases, stops; the core glides a jump (ge) frame by frame (gliding exactly
while it moves, alpha rising, exact at rest), snaps a step (j) and a switch
to insert mid-glide; a terminal's scrolling output lands its cursor; wire
round-trip of the cursor record.

Shared files: src/animation.zig, src/pardes.zig, src/config.zig (toggle
CursorBlink), src/surface.zig, src/detached/wire.zig.

1 files changed, 2 insertions, 0 deletions

diff --git a/docs/config.md b/docs/config.md
index 0332d854..8c986d81 100644
--- a/docs/config.md
+++ b/docs/config.md
@@ -545,6 +545,8 @@ 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 (the default), bouncy or playful
+CursorBlink on   the cursor blinks, solid while typing and half a second
+                 after, eased at each edge, solid after 10 idle seconds
 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)
 ```