Auto-retry on transient provider errors (overloaded, rate limit, 5xx)

- Add retry logic with exponential backoff (2s, 4s, 8s) in AgentSession
- Disable Anthropic SDK built-in retries (maxRetries: 0) to allow app-level handling
- TUI shows retry status with Escape to cancel
- RPC mode: add set_auto_retry, abort_retry commands and auto_retry_start/end events
- Configurable via settings.json: retry.enabled, retry.maxRetries, retry.baseDelayMs
- Exclude context overflow errors from retry (handled by compaction)

fixes #157

packages/coding-agent/src/modes/rpc/rpc-client.ts

@@ -264,6 +264,20 @@ export class RpcClient {
 		await this.send({ type: "set_auto_compaction", enabled });
 	}
 
+	/**
+	 * Set auto-retry enabled/disabled.
+	 */
+	async setAutoRetry(enabled: boolean): Promise<void> {
+		await this.send({ type: "set_auto_retry", enabled });
+	}
+
+	/**
+	 * Abort in-progress retry.
+	 */
+	async abortRetry(): Promise<void> {
+		await this.send({ type: "abort_retry" });
+	}
+
 	/**
 	 * Execute a bash command.
 	 */