Add example builds to CI, document sprite name behavior

- CI: new "Build Examples" job compiles all .ne files and validates
  the output ROMs have correct iNES headers
- Examples: add notes explaining that sprite names (Smiley, Ball) are
  parsed but not yet resolved — all draws use the built-in CHR tile 0.
  Custom sprite declarations come in M3.
- Codegen: explicit `let _ = &draw.sprite_name` to document the
  intentional skip, with comment about M2/M3 scope

https://claude.ai/code/session_01W6eQFStA66EuMKHUFo2rx3

examples/README.md

@@ -35,10 +35,18 @@ Use the d-pad (arrow keys in most emulators) to move the sprite.
 
 ## What you'll see
 
-The ROM displays a small smiley-face sprite (an 8x8 tile built into the
-compiler's default CHR data). In `hello_sprite`, you control it with the d-pad.
+The ROM displays a small 8x8 smiley-face sprite. This is a default tile built
+into the compiler's CHR data. In `hello_sprite`, you control it with the d-pad.
 In `bouncing_ball`, it moves on its own and bounces off the screen edges.
 
+### About sprite names
+
+In Milestone 1, the name in `draw Smiley at: (x, y)` is parsed but not
+resolved to a specific tile — all draws use CHR tile 0 (the built-in smiley).
+The `draw` syntax is forward-compatible: when `sprite` declarations and the
+asset pipeline arrive in M3, names like `Smiley` will reference actual
+sprite definitions with custom tile data from PNGs.
+
 ## Emulator controls
 
 | NES Button | Typical Key |

examples/bouncing_ball.ne

@@ -2,6 +2,10 @@
 //
 // Build:  cargo run -- build examples/bouncing_ball.ne
 // Output: examples/bouncing_ball.nes
+//
+// Note: In M1 the sprite name in `draw` is parsed but not resolved.
+// All sprites use tile 0 from the built-in CHR data (a smiley face).
+// Custom sprite declarations come in M3.
 
 game "Bouncing Ball" {
     mapper: NROM

examples/hello_sprite.ne

@@ -1,8 +1,12 @@
 // Hello Sprite — the simplest NEScript program.
 //
-// Displays a smiley-face sprite on screen and moves it with the d-pad.
+// Displays a sprite on screen and moves it with the d-pad.
 // Build:  cargo run -- build examples/hello_sprite.ne
 // Output: examples/hello_sprite.nes (open in any NES emulator)
+//
+// Note: In M1 the sprite name in `draw` is parsed but not resolved.
+// All sprites use tile 0 from the built-in CHR data (a smiley face).
+// Sprite declarations with custom tile data come in M3.
 
 game "Hello Sprite" {
     mapper: NROM