feat: add typst inline equation preview

Mirrors the existing LaTeX fragment integration but uses the `typst`
CLI to compile `$...$' math fragments into PNGs that are then displayed
inline through the existing kitty-graphics overlay pipeline.

- New section in kitty-graphics.el: customs (typst-command, ppi,
  text-size, preamble), SHA-1 cached PNGs under /tmp/kitty-gfx-typst,
  Emacs face-foreground -> typst rgb() hex conversion.
- Two autoloaded commands: `kitty-gfx-typst-preview' and
  `kitty-gfx-typst-clear-preview', region-aware.
- Regex skips backslash-escaped dollars (\\$not math\\$).
- justfile with recipes: compile/lint/load + per-feature test-* and
  headless typst-render / typst-show.
- tests/test-typst.typ fixture with inline, display, mixed and
  edge-case fragments.
- AGENTS.md updated: test instructions, dependency note, issue marked
  done.

Closes #7. Parent #5.

1 files changed, 31 insertions, 0 deletions

diff --git a/tests/test-typst.typ b/tests/test-typst.typ
new file mode 100644
index 0000000..a28fcbf
--- /dev/null
+++ b/tests/test-typst.typ
@@ -0,0 +1,31 @@
+// Test fixture for kitty-graphics.el typst inline equation preview.
+//
+// Usage:
+//   TERM=xterm-256color emacs -nw -Q -l kitty-graphics.el \
+//     --eval "(kitty-graphics-mode 1)" tests/test-typst.typ
+//   M-x kitty-gfx-typst-preview
+//   M-x kitty-gfx-typst-clear-preview
+//
+// Inline math fragments below should each be replaced by a rendered
+// PNG overlay.  Escaped dollar signs (\$ ... \$) must be ignored.
+
+= Inline samples
+
+Pythagoras: $a^2 + b^2 = c^2$, classic.
+
+Euler: $e^(i pi) + 1 = 0$ -- the famous identity.
+
+Display style with surrounding spaces:
+$ integral_(-oo)^(+oo) e^(-x^2) dif x = sqrt(pi) $
+
+Mixed line: $x = 1$ and $y = 2$ on the same line.
+
+Escaped dollar signs should be skipped: \$not math\$ here.
+
+= Edge cases
+
+Sum: $sum_(k=0)^n binom(n, k) = 2^n$.
+
+Matrix: $mat(1, 2; 3, 4)$.
+
+Greek: $alpha + beta = gamma$.