Post chain: Shadertoy passes compiled by glslc; Crt, Ripple and Glitch rewritten as Shadertoy files

Stage 9 of docs/render-pipeline.md. src/gui/Post.zig runs the chain over
the finished frame: each pass reads the one before, ping-pong textures
between, the last writes the window; an empty chain is the direct path.
The prefix (shaders/post/prefix.glsl) is ghostty's uniform block, name
for name and offset for offset (tested against a copy of its Uniforms, the
selection colours by their GLSL names), at SDL GPU's bindings, y down.

A user's file (Shader <path>) is compiled by glslc with compileGlsl's own
flags on a thread of its own, taken in at the next loop step; errors name
the file's own lines; a failed compile keeps the last good pipeline;
glslc missing is said once. The bundled passes compile with the build,
through the same prefix.

Crt, Ripple and Glitch are Shadertoy files, rewritten: no barrel (input is
identity, tested), everything in linear light and dithered, keyed to iTime.
scene_effects, crt.zig and crt.frag.glsl are gone; the core keeps no clock
for the chain. ShaderAnimation off|on|always drives redraw level A: the
chain alone over the retained frame (34 us CPU a redraw, measured).

Shared files touched: pardes.zig (nextWake loses the scene line,
disableSceneEffects empties the chain, two tests), builtins.zig (one switch
arm), ninep/ctl.zig (two switch arms), macos.zig (flags from the chain),
gui.zig. Not touched: Messages.zig, mouse.zig, detached/*, host_io, tty.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/ninep/ctl.zig b/src/ninep/ctl.zig
index c1f78bab..ed10dd70 100644
--- a/src/ninep/ctl.zig
+++ b/src/ninep/ctl.zig
@@ -263,7 +263,9 @@ fn writeSettings(p: *Pardes, w: *std.Io.Writer) !void {
             // Bare, it names the default directory.
             .dump_dir => if (s.dump_dir.len > 0) try w.print("{s} {s}\n", .{ word, s.dump_dir.get() }) else try w.print("{s}\n", .{word}),
             .transition => |effect| try w.print("{s} {s}\n", .{ word, if (s.panel_transition == effect) "on" else "off" }),
-            .scene => |effect| try w.print("{s} {s}\n", .{ word, if (@field(s.scene_effects, @tagName(effect))) "on" else "off" }),
+            .scene => |effect| try w.print("{s} {s}\n", .{ word, if (s.post.has(effect)) "on" else "off" }),
+            .shader => for (s.post.list()) |entry| if (entry.scene == null) try w.print("{s} {s}\n", .{ word, entry.path.get() }),
+            .shader_animation => try w.print("{s} {s}\n", .{ word, @tagName(s.shader_animation) }),
         }
     }
     try w.writeAll("LocationsConfig ");