fix: skip mixin definitions in codegen to prevent duplicate rendering

Mixin definitions from included files were being rendered as content.
Now generateNode explicitly skips mixin definitions (node.call=false)
while still processing expanded mixin calls.

Bump version to 0.3.12

build.zig.zon

@@ -1,6 +1,6 @@
 .{
     .name = .pugz,
-    .version = "0.3.11",
+    .version = "0.3.12",
     .fingerprint = 0x822db0790e17621d, // Changing this has security and trust implications.
     .minimum_zig_version = "0.15.2",
     .dependencies = .{},

src/tpl_compiler/zig_codegen.zig

@@ -190,6 +190,21 @@ pub const Codegen = struct {
             .Conditional => try self.generateConditional(node),
             .Each, .EachOf => try self.generateEach(node),
             .TypeHint => {}, // Skip - processed during field extraction
+            .Mixin => {
+                // Skip mixin definitions (call=false), only process mixin calls (call=true)
+                // Mixin calls should already be expanded by mixin.expandMixins()
+                if (!node.call) return;
+                // If somehow a mixin call wasn't expanded, process its children
+                for (node.nodes.items) |child| {
+                    try self.generateNode(child);
+                }
+            },
+            .Include => {
+                // Process included content (children were inlined by processIncludes)
+                for (node.nodes.items) |child| {
+                    try self.generateNode(child);
+                }
+            },
             else => {
                 // Unsupported nodes: skip or process children
                 for (node.nodes.items) |child| {