slosh: defaults most people can live in, said by shaders

The out-of-the-box look, rethought as one piece:

- the compiled-in palette calms down: muted blue #7aa2f7 on the same
  neutral darks, with the colours that mean something kept semantic --
  amber bell, red-orange dead. sl0p stays one include away as the house
  style, and contrib/themes/default.kdl is the starting point written
  down (theme-tour shows it).

- derived state defaults now actually follow the theme: the scrolled
  wash is rebuilt from scroll_bg after the theme block (it used to bake
  the compiled accent), and declaring a state -- in any file of an
  include chain -- still wins. The dump writes derived states as
  comments so C-a e cannot pin what is meant to keep following.

- a bell you can see: the frame blinks three times in theme's bell
  colour then breathes until answered, and a soft diagonal shimmer --
  the bell colour halved towards default_fg, width breathing on a sine
  -- crosses the body for the same 900ms. bell_indicator false silences
  all of it; states { bell { } } replaces it like any state. since
  carries the clock dependency, so an idle session pays nothing.

- scrollback says where it continues: while scrolled, the viewport's
  top and bottom rows melt towards an edge with content past it and
  turn solid at the buffer's end. New expression variables above/below
  (lines hidden past each edge, own dependency bit, cached per scroll
  position), carried in shade_ctx_t -- SLOSH_SHADER_ABI 3 -> 4.

- expressions survive the dump: a program keeps its source and cb_chain
  writes it back, so amount="(y % 2) * 40" no longer dumps as a number.

- headers move to include/, -Iinclude everywhere; the plugin Makefile's
  SLOSH var becomes SLOSH_DIR because slosh exports SLOSH=1 into every
  pane it runs, and building from inside a session read that as a path.

- comment drift culled where features outran the prose, and the
  derivation boilerplate folded into derived_pass()/ctx_scroll().

1 files changed, 13 insertions, 0 deletions

diff --git a/include/cmd.h b/include/cmd.h
new file mode 100644
index 0000000..a54505d
--- /dev/null
+++ b/include/cmd.h
@@ -0,0 +1,13 @@
+/* The command vocabulary, shared by the headless driver and the control
+ * socket, so a script written against one works against the other. */
+#ifndef SLOSH_CMD_H
+#define SLOSH_CMD_H
+
+#include "app.h"
+
+/* Execute one command line. Returns a freshly allocated reply (possibly an
+ * empty string), or NULL if the command is unknown. Sets *quit for "quit". */
+char *cmd_exec(app_t *a, screen_t *s, input_parser_t *in, const char *line,
+               bool *quit);
+
+#endif /* SLOSH_CMD_H */