🔧 Fix LLVM basic block naming collision (ChatGPT5)

- Add function name prefix to basic block labels to avoid cross-function conflicts
- blocks.rs: create_basic_blocks now takes fn_label parameter
- Format: 'Main_join_2_bb23' instead of just 'bb23'
- Add conservative fallback for missing terminators (jump to next or entry)
- This fixes 'Basic Block does not have terminator' verification error

Analysis insights:
- MIR output was correct (all blocks had terminators)
- Problem was LLVM-side block name collision between functions
- Classic case of 'Rust complexity' - simple C++ style fix works best
- Sometimes the simplest solution is the right one\!

src/backend/llvm/compiler/codegen/instructions/blocks.rs

@@ -11,18 +11,19 @@ pub(in super::super) fn create_basic_blocks<'ctx>(
     codegen: &CodegenContext<'ctx>,
     llvm_func: FunctionValue<'ctx>,
     func: &MirFunction,
+    fn_label: &str,
 ) -> (HashMap<BasicBlockId, BasicBlock<'ctx>>, BasicBlock<'ctx>) {
     let mut bb_map: HashMap<BasicBlockId, BasicBlock> = HashMap::new();
     let entry_first = func.entry_block;
     let entry_bb = codegen
         .context
-        .append_basic_block(llvm_func, &format!("bb{}", entry_first.as_u32()));
+        .append_basic_block(llvm_func, &format!("{}_bb{}", fn_label, entry_first.as_u32()));
     bb_map.insert(entry_first, entry_bb);
     for bid in func.block_ids() {
         if bid == entry_first {
             continue;
         }
-        let name = format!("bb{}", bid.as_u32());
+        let name = format!("{}_bb{}", fn_label, bid.as_u32());
         let bb = codegen.context.append_basic_block(llvm_func, &name);
         bb_map.insert(bid, bb);
     }