G5: lapis, 0x4200.cafe's manuscript, as a theme with its ornament

A native theme `lapis` (src/themes/lapis.zig) from web/theme/lapis.css:
a lapis-deep page, lapis tags with gold names, vellum text, vermilion
rubrics, gold rules and a vermilion tag rule, gold selection in lapis ink.
Its ornament is the theme's new `decor` (colors.Decor), drawn by a pixel
shell inside the chrome it already has (decision 1), all of it off every
focus indicator:

- page_dots: the site's gold dot grid (#e8c46a22, 22 px), drawn by the
  cell shader on page-coloured cells alone (flag 0x10000000), so it lies
  under the text and never under a selection, a tag or the cursor; fixed
  to the window, a page the panes lie on.
- rail_checker: the dither frame's gold and lapis checker in the scroll
  track (a decor kind, flag 0x08000000), anchored to its rail; the thumb
  stays solid gold.
- tag plaques (tag_border, tag_shadow, tag_stripe): every tag a raised
  plaque inside its own band, the site's trail: a 2px gold frame and a
  hard 5px vermilion shadow down and right, both within the band's rows
  and columns (down, what the slack under the text leaves), so no shadow
  reaches a body, a grip or the next pane. The focused pane's plaque is
  the code window's title bar, gold and lapis stripes of 2px, its words
  on plates of the focused ground; unfocused ones are plain; column and
  workspace tags take the object-label language (1px frame, 2px shadow
  toward the page). Drawn as decor under the cells (a group's under
  range), with blank tag cells see-through and the cells blended
  premultiplied (pipeline_over) on such frames; opaque windows only.
- title_shadow: the titles' vermilion offset shadow under a file name's
  letters, sampled in the cell shader inside the letters' own cells (flag
  0x08000000), none on a cursor.

Chrome carries the decor (decor_*, name_ink, active_name_ink); a theme
file folds a nested decor literal field by field. Left out, with why, in
docs/effects.md: the fonts, the ornaments, a decor crossfade, and in the
tty anything but the colours (a tag row has no spare cell for a shadow).
An empty column is the page. The effect id is masked to 27 bits (ui.vert/ui.frag) for the
fifth flag.

Tests: the cell flags land only on page ground and file-name cells, never
a cursor, nothing without decor; lapis's plaques stay inside their tag's
band, clear of every grip, only the focused one striped; its checker is in
the track; no other theme draws any; the separator and focus
tests cover lapis. Goldens: theme and themesel (the ring gains lapis after
acme). Gates as G4. Feel review: .scratch/render/lapis/ (lapis.png, lapis-2x.png,
tags-focused-vs-unfocused-2x.png, a PanelSlide at 60 fps and a quarter).

1 files changed, 1 insertions, 0 deletions

diff --git a/docs/themes.md b/docs/themes.md
index 2b15051e..38596819 100644
--- a/docs/themes.md
+++ b/docs/themes.md
@@ -121,6 +121,7 @@ so existing exported themes remain valid.
 | `rule_px` | Pixel shells: the width of the rules between columns, between panes stacked in a column, and under the workspace and column tags, in `border` (the rule between a tag and its body is always one pixel), in logical pixels: doubled on a 2x display, as acme scales its Border | 2 |
 | `box_border`, `box_dirty` | The grip is acme's button: `box` filled when focused, else a two-pixel ring of `box_border` round the tag's ground; `box_dirty` fills it inside either ring while its file is unsaved (a grid, which has no ring, shows a bold `*` on `box_dirty` in the grip's second cell) | `box_dim`; `diagnostic_warning`, then `num` |
 | `rail_px` | Pixel shells: the scroll column's width, the grip's button over the scrollbar (thumb a pixel narrower), in pixels at a 17px tagline, scaled with it | 12, acme's Scrollwid |
+| `decor` | Pixel shells: a theme's ornament, drawn inside the chrome it has (lapis's): `page_dots` (a dot grid on the page's own ground, `page_dot_alpha` strong every `page_dot_px`), `rail_checker` (a checker in the scroll track, squares of `rail_checker_px`), `tag_border`, `tag_shadow`, `tag_stripe` (every tag a raised plaque inside its own band: a `tag_border_px` frame round its text and a hard `tag_shadow_px` shadow down and right, both inside the band's rows and columns; the focused pane's plaque striped `tag_stripe_px` with its words on plates of the tag's ground; column and workspace tags a quieter one; opaque windows only) and `title_shadow` (the file name's offset shadow, `title_shadow_px`), sizes in logical pixels. None of it touches a focus indicator | none |
 
 Native palettes give filenames a distinct hue at approximately the same
 brightness as the surrounding tag text. This also applies to output names