### Purpose
Build a competitive 2-player falling block puzzle game that runs in the browser.

### Game Design

**Visual Style**
- Clean, colorful block graphics
- Split-screen layout: Player 1 on left, Player 2 on right
- Each player has their own 10x20 grid
- Ghost piece showing where block will land
- Next piece preview for each player
- Score and lines cleared displayed per player

**Block Pieces (7 Shapes)**
- I-piece (cyan): 4 blocks in a line
- O-piece (yellow): 2x2 square
- T-piece (purple): T-shape
- S-piece (green): S-shape zigzag
- Z-piece (red): Z-shape zigzag
- J-piece (blue): J-shape
- L-piece (orange): L-shape

**Core Mechanics**
- Blocks fall from top of grid
- Player moves blocks left/right, rotates, and soft/hard drops
- Completed horizontal lines clear and award points
- Game speeds up as more lines are cleared
- Game over when blocks stack to the top

**Competitive Mechanic - Garbage Lines**
- Clearing 2 lines: Send 1 garbage line to opponent
- Clearing 3 lines: Send 2 garbage lines to opponent
- Clearing 4 lines: Send 4 garbage lines to opponent
- Garbage lines appear at bottom of opponent's grid with one random gap
- Visual warning when garbage is incoming

**Scoring**
- 1 line: 100 points
- 2 lines: 300 points
- 3 lines: 500 points
- 4 lines: 800 points
- Bonus for back-to-back multi-line clears

**Game Flow**
- Start screen with "PRESS START" - shows controls for both players
- Countdown "3, 2, 1, GO!" before match starts
- Match ends when one player tops out
- Winner announcement with final scores
- "PLAY AGAIN" option

### Controls

**Keyboard - Player 1 (Left Side)**
- A/D: Move left/right
- W: Rotate clockwise
- S: Soft drop (faster fall)
- Q: Rotate counter-clockwise
- Space: Hard drop (instant)

**Keyboard - Player 2 (Right Side)**
- Left/Right arrows: Move left/right
- Up arrow: Rotate clockwise
- Down arrow: Soft drop
- Period (.): Rotate counter-clockwise
- Enter: Hard drop

**Gamepad Support (IMPORTANT)**
The entire game must be playable with gamepad controllers, including menus:
- Use the Gamepad API: https://developer.mozilla.org/en-US/docs/Web/API/Gamepad_API
- First connected gamepad = Player 1
- Second connected gamepad = Player 2
- D-pad or Left stick: Move piece left/right, soft drop (down)
- A button (buttons[0]): Rotate clockwise
- B button (buttons[1]): Rotate counter-clockwise
- X button (buttons[2]): Hard drop
- Start button (buttons[9]): Start game / Pause
- A button on start screen: Ready up (both players must ready)
- A button on game over: Play again
- Show "P1 Gamepad Connected" / "P2 Gamepad Connected" messages
- Poll gamepad state in game loop using `navigator.getGamepads()`

### Technical Notes
- Use HTML5 Canvas for rendering
- 60 FPS game loop with requestAnimationFrame
- Independent game state for each player
- Responsive canvas that scales to fit screen
- No external dependencies needed