Reorganize src/ directory into feature/domain-based structure

Restructure flat src/ directory (17 files) into organized folders:

Structure:
- src/core/ - Main API (rondevu.ts, offer-pool.ts, types.ts, index.ts)
- src/connections/ - WebRTC connections (base.ts, offerer.ts, answerer.ts, config.ts, events.ts)
- src/api/ - HTTP layer (client.ts, batcher.ts)
- src/crypto/ - Crypto adapters (adapter.ts, node.ts, web.ts)
- src/utils/ - Utilities (async-lock.ts, exponential-backoff.ts, message-buffer.ts)

Changes:
- Move all 17 files to appropriate feature folders
- Update all import paths to reflect new structure
- Update package.json main/types to point to dist/core/index.js
- Preserve git history with git mv

Benefits:
- Clear separation of concerns
- Easier navigation and maintenance
- Better scalability for future features
- Logical grouping of related files

🤖 Generated with Claude Code

src/utils/exponential-backoff.ts

@@ -0,0 +1,59 @@
+/**
+ * Exponential backoff utility for connection reconnection
+ */
+
+export interface BackoffConfig {
+    base: number        // Base delay in milliseconds
+    max: number         // Maximum delay in milliseconds
+    jitter: number      // Jitter factor (0-1) to add randomness
+}
+
+export class ExponentialBackoff {
+    private attempt: number = 0
+
+    constructor(private config: BackoffConfig) {
+        if (config.jitter < 0 || config.jitter > 1) {
+            throw new Error('Jitter must be between 0 and 1')
+        }
+    }
+
+    /**
+     * Calculate the next delay based on the current attempt number
+     * Formula: min(base * 2^attempt, max) with jitter
+     */
+    next(): number {
+        const exponentialDelay = this.config.base * Math.pow(2, this.attempt)
+        const cappedDelay = Math.min(exponentialDelay, this.config.max)
+
+        // Add jitter: delay ± (jitter * delay)
+        const jitterAmount = cappedDelay * this.config.jitter
+        const jitter = (Math.random() * 2 - 1) * jitterAmount // Random value between -jitterAmount and +jitterAmount
+        const finalDelay = Math.max(0, cappedDelay + jitter)
+
+        this.attempt++
+        return Math.round(finalDelay)
+    }
+
+    /**
+     * Get the current attempt number
+     */
+    getAttempt(): number {
+        return this.attempt
+    }
+
+    /**
+     * Reset the backoff state
+     */
+    reset(): void {
+        this.attempt = 0
+    }
+
+    /**
+     * Peek at what the next delay would be without incrementing
+     */
+    peek(): number {
+        const exponentialDelay = this.config.base * Math.pow(2, this.attempt)
+        const cappedDelay = Math.min(exponentialDelay, this.config.max)
+        return cappedDelay
+    }
+}