Implement stuck snake mechanics, persistent colors, and length display

Major gameplay changes:
- Snakes no longer die from collisions
- When blocked, snakes get "stuck" - head stays in place, tail shrinks by 1 per tick
- Snakes auto-unstick when obstacle clears (other snakes move/shrink away)
- Minimum snake length is 1 (head-only)
- Game runs continuously without rounds or game-over state

Color system:
- Each player gets a persistent color for their entire connection
- Colors assigned on join, rotate through available colors
- Color follows player even after disconnect/reconnect
- Works for both desktop and web clients

Display improvements:
- Show snake length instead of score
- Length accurately reflects current snake size
- Updates in real-time as snakes grow/shrink

Server fixes:
- Fixed HTTP server initialization issues
- Changed default host to 0.0.0.0 for network multiplayer
- Improved file serving with proper routing

Testing:
- Updated all collision tests for stuck mechanics
- Added tests for stuck/unstick behavior
- Added tests for color persistence
- All 12 tests passing

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

web/game.js

@@ -229,8 +229,8 @@ class GameClient {
 
             // Draw snakes
             if (this.gameState.snakes) {
-                this.gameState.snakes.forEach((snake, index) => {
-                    const color = this.COLOR_SNAKES[index % this.COLOR_SNAKES.length];
+                this.gameState.snakes.forEach((snake) => {
+                    const color = this.COLOR_SNAKES[snake.color_index % this.COLOR_SNAKES.length];
 
                     if (snake.body && snake.alive) {
                         // Draw body
@@ -314,10 +314,10 @@ class GameClient {
 
         this.playersList.innerHTML = '';
 
-        this.gameState.snakes.forEach((snake, index) => {
+        this.gameState.snakes.forEach((snake) => {
             const playerItem = document.createElement('div');
             playerItem.className = `player-item ${snake.alive ? 'alive' : 'dead'}`;
-            playerItem.style.borderLeftColor = this.COLOR_SNAKES[index % this.COLOR_SNAKES.length];
+            playerItem.style.borderLeftColor = this.COLOR_SNAKES[snake.color_index % this.COLOR_SNAKES.length];
 
             const nameSpan = document.createElement('span');
             nameSpan.className = 'player-name';
@@ -327,7 +327,7 @@ class GameClient {
 
             const scoreSpan = document.createElement('span');
             scoreSpan.className = 'player-score';
-            scoreSpan.textContent = snake.score;
+            scoreSpan.textContent = snake.body.length;
 
             playerItem.appendChild(nameSpan);
             playerItem.appendChild(scoreSpan);