feat: switch from C to LLVM IR code generation

- Replace all C code generation with LLVM IR (flat DFA model with
  bb_ prefix labels to avoid SSA value name collisions)
- Remove c.min.js, add llvm.min.js highlight.js language definition
- Update shell.nix: gcc -> clang, remove sdl3/mesa deps
- Download LLVM Language Reference to docs/llvm/LangRef.html
- Rename #c-code to #ir-code in HTML, JS, and CSS
- Replace _generateIncludes with _generateLLVMDecls for extern
  function declarations using LLVM_DECL_MAP
- Add string pool (CodeGen.allocString, stringGlobal, llvmStringArg)
  for LLVM IR global string constants with getelementptr references

wcprogram.js

@@ -190,29 +190,27 @@ class WCProgram extends HTMLElement {
     return { boolDefs, scalarDefs, vectorDefs, stringDefs, arrayDefs };
   }
 
-  _generateIncludes(proccalls, hasStrings) {
-    const libNames = new Set();
-    for (const p of proccalls) {
-      const qname = p._selectedProc;
-      if (qname) {
-        const lib = qname.split("/")[0];
-        if (lib) libNames.add(lib);
+  _generateLLVMDecls(proccalls) {
+    var seen = new Set();
+    var lines = [];
+    for (var pi = 0; pi < proccalls.length; pi++) {
+      var qname = proccalls[pi]._selectedProc;
+      if (!qname || seen.has(qname)) continue;
+      seen.add(qname);
+      var decl = LLVM_DECL_MAP[qname];
+      if (decl) {
+        lines.push(decl);
+      } else {
+        var fn = qname.split("/")[1] || qname;
+        lines.push("declare i32 @" + fn + "(...)");
       }
     }
-    let includes = Array.from(libNames).map(l => {
-      const path = INCLUDE_MAP[l] || (l + ".h");
-      return `#include <${path}>`;
-    }).join("\n");
-    if (hasStrings) {
-      const hdr = "#include <stdlib.h>\n#include <string.h>";
-      includes = includes ? includes + "\n" + hdr : hdr;
-    }
-    return includes;
+    return lines.join("\n");
   }
 
   generateCode() {
-    const outputEl = $id("c-code");
-    if (!outputEl) { showError("Missing #c-code output element"); return; }
+    const outputEl = $id("ir-code");
+    if (!outputEl) { showError("Missing #ir-code output element"); return; }
 
     const { usedQuantities, usedUnits } = this._gatherUsedTypes();
 
@@ -220,51 +218,46 @@ class WCProgram extends HTMLElement {
     const unitDefs = this._generateUnitDefs(usedUnits);
     const { boolDefs, scalarDefs, vectorDefs, stringDefs, arrayDefs } = this._generateVariableDeclarations();
 
-    const hasStrings = $id("variable-area").querySelectorAll("wc-string").length > 0;
-    const stringStruct = hasStrings
-      ? "typedef struct { char *data; long int length; } string;\n\n"
-      : "";
+    CodeGen.resetStringPool();
 
     const firstChild = this.firstElementChild;
     const body = firstChild && typeof CodeGen.emitFlat === "function"
       ? CodeGen.emitFlat(firstChild)
-      : "\n// (no flowchart body)\n";
-    const proccalls  = this.querySelectorAll("wc-proccall");
-    const includes   = this._generateIncludes(proccalls, hasStrings);
+      : "; no flowchart body\n";
 
+    // Collect external function declarations from used libraries
+    const proccalls = this.querySelectorAll("wc-proccall");
+    const decls = this._generateLLVMDecls(proccalls);
+
+    // Collect string globals
+    const strPool = CodeGen.getStringPool();
+    const globals = strPool.map(function (_, i) { return CodeGen.stringGlobal(i); }).join("\n");
+
+    // Variable declarations -> alloca instructions in the prologue
     const dataSection = (boolDefs || scalarDefs || vectorDefs || stringDefs || arrayDefs)
       ? [boolDefs, scalarDefs, vectorDefs, stringDefs, arrayDefs]
-          .filter(Boolean).map(s => s + "\n").join("")
+          .filter(Boolean).map(function (s) { return s + "\n"; }).join("")
       : "";
 
-    const hasReturnOrExit =
-      body.includes("\n  return ") || body.includes("\n  exit(");
-    const raw =
-      "// --- WiseCode\u00ae ---\n" +
-      (includes ? includes + "\n\n" : "") +
-      "int main() {\n" +
-      (typeDefs ? typeDefs + "\n\n" : "") +
-      (unitDefs ? unitDefs + "\n\n" : "") +
-      stringStruct + dataSection + body +
-      (hasReturnOrExit ? "" : "return 0;\n") +
-      "}\n// --- END ---";
+    const raw = CodeGen.generateIRFile(firstChild, decls, globals, dataSection);
     outputEl.textContent = raw;
     if (typeof hljs !== "undefined") hljs.highlightElement(outputEl);
-    outputEl.parentElement.dataset.language = "c";
+    outputEl.parentElement.dataset.language = "llvm";
   }
 }
 
 
 /**
- * Maps library names to their C #include paths.
- * Libraries not listed here use the default `<{name}.h>` convention.
+ * Maps library/function names to their LLVM IR `declare` signature.
+ * Key is the proc qname, value is the declare line.
+ * Functions not listed get a generic `declare i32 @name(...)`.
  */
-const INCLUDE_MAP = {
-  "sdl3":  "SDL3/SDL.h",
-  "glfw":  "GLFW/glfw3.h",
-  "gl":    "GL/gl.h",
+const LLVM_DECL_MAP = {
+  "stdio/printf": "declare i32 @printf(i8*, ...)",
+  "stdlib/exit":  "declare void @exit(i32)",
 };
 
+
 // ═══════════════════════════════════════════════════════════════════════════════
 //  Block registry
 // ═══════════════════════════════════════════════════════════════════════════════