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

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 All notable changes to this project will be documented in this file.
 
+## [0.0.7] - Unreleased
+
+### Added
+- 3-operator FM synthesis words: `fm2` (operator 2 depth), `fm2h` (operator 2 harmonic ratio), `fmalgo` (algorithm: 0=cascade, 1=parallel, 2=branch), `fmfb` (feedback amount). Extends the existing 2-OP FM engine to a full 3-OP architecture with configurable routing and operator feedback.
+
 ## [0.0.6] - 2026-05-02
 
 ### Added

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",