glm(win): ignore cmd.exe's built-in PROMPT template; add COLI_PROMPT (#271)

Windows cmd.exe always exports PROMPT (its prompt template, default "$P$G")
into a child's environment. The engine's `getenv("PROMPT")` picked that up, so
running `glm.exe` from cmd for the oracle self-test instead entered text-
generation mode — loading a tokenizer the tiny model doesn't ship and failing
with "tokenizer.json: No such file". PowerShell has no PROMPT env var, so it
worked there (galmok's 32/32) but not in cmd — same command, different shell.

New coli_user_prompt(): honors COLI_PROMPT everywhere, and on Windows ignores a
PROMPT that carries cmd's $-metacodes ($P,$G,...) — a real prompt has none. cmd
users can still pass a prompt via COLI_PROMPT or a non-$ PROMPT. Verified: $P$G
-> oracle mode, "Explain recursion" -> honored, COLI_PROMPT -> honored.

Third native-Windows bug surfaced by a from-scratch main download (after the
-lpsapi link fix and the bilingual oracle message).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

c/glm.c

@@ -5485,6 +5485,24 @@ static void cap_for_ram(Model *m, double ram_gb, int ebits, int max_ctx){
     }
 }
 
+/* The user's generation prompt. COLI_PROMPT is honored on every platform; a bare
+ * PROMPT is honored too, EXCEPT on Windows, where cmd.exe always exports its own
+ * PROMPT template (default "$P$G", the thing that draws "C:\...>") into the child's
+ * environment. That is a shell UI string, not a prompt: taking it would send the
+ * engine into text-generation mode (needing a tokenizer) instead of the oracle
+ * self-test, and would "generate" from "$P$G". So on Windows a PROMPT carrying
+ * cmd's $-metacodes is ignored; set COLI_PROMPT to pass a real prompt from cmd. */
+static const char *coli_user_prompt(void){
+    const char *p = getenv("COLI_PROMPT");
+    if(p) return p;
+    p = getenv("PROMPT");
+#ifdef _WIN32
+    if(p) for(const char *q=p; q[0]; q++)
+        if(q[0]=='$' && q[1] && strchr("ABCDEFGHLNPQSTV_+|$", q[1]&~0x20)){ p=NULL; break; }
+#endif
+    return p;
+}
+
 int main(int argc, char **argv){
     /* ---- Permanent OpenMP hot-thread tuning. The per-expert matmul regions are
      * tiny and back-to-back; with the default passive wait policy libgomp parks
@@ -5750,9 +5768,10 @@ int main(int argc, char **argv){
     }
 
     /* modo testo reale: PROMPT="..." [NGEN=n] -> tokenizza, genera, detokenizza */
-    if(getenv("PROMPT")){
+    const char *user_prompt = coli_user_prompt();   /* ignores cmd.exe's PROMPT template (#271) */
+    if(user_prompt){
         int ngen=getenv("NGEN")?atoi(getenv("NGEN")):64;
-        run_text(&m, snap, getenv("PROMPT"), ngen);
+        run_text(&m, snap, user_prompt, ngen);
         if(stats) stats_dump(&m,stats);
         return 0;
     }