### Purpose
Build a classic 8-bit style space shooter arcade game that runs in the browser.

### Game Design

**Visual Style**
- Retro 8-bit pixel art aesthetic
- Starfield background scrolling vertically
- Pixelated player ship, enemies, and projectiles
- Screen shake on explosions
- Retro color palette (limited colors like NES/arcade)

**Player Ship**
- Positioned at bottom of screen
- Smooth movement in all directions
- Firing laser projectiles upward
- 3 lives, shown as ship icons
- Brief invincibility after getting hit (flashing effect)

**Enemies**
- Multiple enemy types with different movement patterns
- Basic enemies: move down in formation
- Zigzag enemies: move side to side while descending
- Fast enemies: quick dive attacks
- Enemies spawn in waves, increasing difficulty

**Combat & Effects**
- When projectile hits enemy: enemy explodes with particle explosion effect
- When enemy hits player: player explodes, loses a life, respawns with invincibility
- Explosion animation: pixelated burst, expanding then fading
- Sound effects: 8-bit style pew-pew, explosions, power-up pickup

**Power-ups**
- Dropped randomly by destroyed enemies
- Double shot: fire two projectiles
- Speed boost: faster movement
- Shield: absorbs one hit
- Power-ups last 10 seconds

**Scoring**
- Points per enemy destroyed (10, 25, 50 based on type)
- Bonus points for wave completion
- High score saved to localStorage
- Score displayed at top of screen

**Game Flow**
- Start screen with "PRESS START" flashing
- Wave number displayed at start of each wave
- Game over screen showing final score and high score
- "PLAY AGAIN" option

### Controls

**Keyboard**
- Arrow keys: Move ship (up, down, left, right)
- Space: Fire weapon
- Enter: Start game / Restart

**Gamepad Support (IMPORTANT)**
The entire game must be playable with a gamepad controller, including menus:
- Use the Gamepad API: https://developer.mozilla.org/en-US/docs/Web/API/Gamepad_API
- Left analog stick: Move ship
- A button (buttons[0]): Fire weapon
- Start button (buttons[9]): Start game / Pause
- A button on start screen: Begin game
- A button on game over screen: Play again
- Poll gamepad state in game loop using `navigator.getGamepads()`
- Show "Gamepad Connected" message when controller detected

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