Feat: introduce Forth words for 3-OP Fm synthesis (with feedback)

crates/forth/src/words/sound.rs

@@ -457,6 +457,46 @@ pub(super) const WORDS: &[Word] = &[
         compile: Param,
         varargs: false,
     },
+    Word {
+        name: "fm2",
+        aliases: &[],
+        category: "FM",
+        stack: "(f --)",
+        desc: "Set FM operator 2 depth",
+        example: "1.5 fm2",
+        compile: Param,
+        varargs: false,
+    },
+    Word {
+        name: "fm2h",
+        aliases: &[],
+        category: "FM",
+        stack: "(f --)",
+        desc: "Set FM operator 2 harmonic ratio",
+        example: "3 fm2h",
+        compile: Param,
+        varargs: false,
+    },
+    Word {
+        name: "fmalgo",
+        aliases: &[],
+        category: "FM",
+        stack: "(n --)",
+        desc: "Set FM algorithm (0=cascade 1=parallel 2=branch)",
+        example: "0 fmalgo",
+        compile: Param,
+        varargs: false,
+    },
+    Word {
+        name: "fmfb",
+        aliases: &[],
+        category: "FM",
+        stack: "(f --)",
+        desc: "Set FM feedback amount",
+        example: "0.5 fmfb",
+        compile: Param,
+        varargs: false,
+    },
     // Modulation
     Word {
         name: "vib",