Initial CST-Agent: portable Linux/Termux/Windows coding agent.

Vendored sashidown, OpenAI-compatible env (OPENAI_*), and bootstrap scripts.

Co-authored-by: Cursor <cursoragent@cursor.com>

vendor/sashidown/src/ansi_style.h

@@ -0,0 +1,48 @@
+#ifndef SASHIDOWN_ANSI_STYLE_H
+#define SASHIDOWN_ANSI_STYLE_H
+
+/* Built-in ANSI role styles (SGR). Strings are compile-time literals. */
+
+typedef struct {
+    const char *reset;
+
+    const char *heading[7]; /* [1..6] used; [0] unused */
+    const char *heading_end;
+
+    const char *strong_on;
+    const char *strong_off;
+    const char *emph_on;
+    const char *emph_off;
+    const char *strike_on;
+    const char *strike_off;
+
+    const char *code_on;
+    const char *code_off;
+    const char *fence_on;
+    const char *fence_off;
+
+    const char *link_on;
+    const char *link_off;
+    const char *url_on;
+    const char *url_off;
+    const char *image_on;
+    const char *image_off;
+
+    const char *bullet;
+    const char *bullet_end;
+    const char *ol_on;
+    const char *ol_off;
+
+    const char *bq_prefix;
+    const char *th_on;
+    const char *th_off;
+    const char *sep; /* table column separator */
+
+    const char *latex_on;
+    const char *latex_off;
+} ansi_theme_t;
+
+const ansi_theme_t *ansi_theme_color(void);
+const ansi_theme_t *ansi_theme_plain(void);
+
+#endif