IR codegen: state dispatch, multi-OAM, and transition support

State machine dispatch:
- IrProgram now stores states (Vec<String>) and start_state
- Lowering captures state metadata before walking the AST
- IR codegen generates a main loop with vblank wait and CMP+BNE+JMP
  dispatch table, matching the AST codegen's layout
- Each frame handler ends with JMP __ir_main_loop
- current_state initialized to the start state's index at boot

Multi-OAM support:
- next_oam_slot counter, reset at the start of each _frame function
- Sequential allocation of 4-byte OAM entries at $0200 + slot*4
- Silently drops draws beyond slot 63 (OAM full)

Transition codegen:
- IrOp::Transition now looks up the target state's index from
  state_indices, writes it to ZP $03, and JMPs back to main loop
- Previously this was a no-op placeholder

Shared constants:
- ZP_FRAME_FLAG ($00) and ZP_CURRENT_STATE ($03) match AST codegen

Tests: 271 total (5 new IR codegen tests + 2 new integration tests)
All 7 examples compile through --use-ir, including multi-state games
and programs with transitions and functions.

https://claude.ai/code/session_01W6eQFStA66EuMKHUFo2rx3

src/ir/lowering.rs

@@ -26,6 +26,9 @@ struct LoweringContext {
     current_label: String,
     // Loop context for break/continue
     loop_stack: Vec<LoopContext>,
+    // State metadata captured from the AST
+    state_names: Vec<String>,
+    start_state: String,
 }
 
 struct LoopContext {
@@ -57,6 +60,8 @@ impl LoweringContext {
             current_ops: Vec::new(),
             current_label: String::new(),
             loop_stack: Vec::new(),
+            state_names: Vec::new(),
+            start_state: String::new(),
         }
     }
 
@@ -104,10 +109,16 @@ impl LoweringContext {
             functions: self.functions,
             globals: self.globals,
             rom_data: self.rom_data,
+            states: self.state_names,
+            start_state: self.start_state,
         }
     }
 
     fn lower_program(&mut self, program: &Program) {
+        // Capture state metadata before lowering
+        self.state_names = program.states.iter().map(|s| s.name.clone()).collect();
+        program.start_state.clone_into(&mut self.start_state);
+
         // Register constants
         for c in &program.constants {
             if let Expr::IntLiteral(v, _) = &c.value {