feat: add round-robin rotation and cooldown for auth profiles

Adds usage tracking to auth profiles for automatic rotation:

- ProfileUsageStats type with lastUsed, cooldownUntil, errorCount
- markAuthProfileUsed(): tracks successful usage, resets errors
- markAuthProfileCooldown(): applies exponential backoff (1/5/25/60min)
- isProfileInCooldown(): checks if profile should be skipped
- orderProfilesByMode(): now sorts by lastUsed (oldest first)

On auth/rate-limit failures, profiles are marked for cooldown before
rotation. On success, usage is recorded for round-robin ordering.

This enables automatic load distribution across multiple accounts
(e.g., Antigravity 5-hour rate limit windows).

src/agents/pi-embedded-runner.ts

@@ -24,7 +24,7 @@ import {
 } from "../process/command-queue.js";
 import { resolveUserPath } from "../utils.js";
 import { resolveClawdbotAgentDir } from "./agent-paths.js";
-import { markAuthProfileGood } from "./auth-profiles.js";
+import { markAuthProfileGood, markAuthProfileUsed, markAuthProfileCooldown } from "./auth-profiles.js";
 import type { BashElevatedDefaults } from "./bash-tools.js";
 import { DEFAULT_MODEL, DEFAULT_PROVIDER } from "./defaults.js";
 import {
@@ -954,6 +954,10 @@ export async function runEmbeddedPiAgent(params: {
           const authFailure = isAuthAssistantError(lastAssistant);
           const rateLimitFailure = isRateLimitAssistantError(lastAssistant);
           if (!aborted && (authFailure || rateLimitFailure)) {
+            // Mark current profile for cooldown before rotating
+            if (lastProfileId) {
+              markAuthProfileCooldown({ store: authStore, profileId: lastProfileId });
+            }
             const rotated = await advanceAuthProfile();
             if (rotated) {
               continue;
@@ -1040,6 +1044,8 @@ export async function runEmbeddedPiAgent(params: {
               provider,
               profileId: lastProfileId,
             });
+            // Track usage for round-robin rotation
+            markAuthProfileUsed({ store: authStore, profileId: lastProfileId });
           }
           return {
             payloads: payloads.length ? payloads : undefined,