fix: Multi-account rotation bugs, performance improvements, and enhanced test coverage

[ndycode]

Summary

This PR contains comprehensive fixes for multi-account rotation bugs, significant performance improvements, enhanced error handling, and expanded test coverage.

Bug Fixes

• True round-robin rotation: Accounts now rotate on every request, not just on rate-limit failover
• Independent per-family cursors: Added cursorByFamily to prevent cross-family interference when switching accounts
• Fixed markSwitched() bug: Removed incorrect call after rate-limiting that pointed back to blocked account
• Fixed cursor indexing: Cursor now indexes into accounts array directly for consistent round-robin behavior

Performance Improvements

• Async I/O + memory caching: Converted sync I/O to async in lib/prompts/codex.ts with in-memory caching
• Debounced saves: Added saveToDiskDebounced() and flushPendingSave() methods to reduce disk writes
• Parallel hydration: Changed hydrateEmails() from sequential loop to Promise.all
• Removed redundant calls: Eliminated duplicate loadAccounts() call, added hasRefreshToken() method
• Single body read: Refactored handleErrorResponse() to read response body once with safeReadBody()

Error Handling Improvements

• Detailed token failure info: Added TokenFailureReason type with reasons: http_error, invalid_response, network_error, missing_refresh, unknown
• Logging for catch blocks: Added logging to 8 previously swallowed catch blocks
• Extended OAuth timeout: Increased poll timeout from 60s to 5 minutes

Race Condition Fix

• Storage mutex: Added withStorageLock() pattern in lib/storage.ts for concurrent write safety

New Test Coverage (+81 tests)

Test File	Tests	Coverage
test/cli.test.ts	17	CLI module with mocked readline
test/model-map.test.ts	20	Model mapping functions
test/storage-async.test.ts	23	Storage async operations
test/rotation-integration.test.ts	21	Multi-account rotation scenarios
test/accounts.test.ts	+3	New rotation tests

Verification

• ✅ Build: Clean (tsc)
• ✅ Tests: 331 passed (was 250, +32% coverage)
• ✅ Lint: Clean (eslint)

Files Changed

• index.ts - Debounced saves, parallel hydration, improved error handling
• lib/accounts.ts - Per-family cursors, true round-robin, debounced save methods
• lib/auth/auth.ts - Detailed token failure reasons
• lib/auth/server.ts - Extended timeout, improved logging
• lib/prompts/codex.ts - Async I/O with memory caching
• lib/request/fetch-helpers.ts - Single body read optimization
• lib/storage.ts - Mutex for concurrent writes
• lib/types.ts - TokenFailureReason type
• 4 new test files + updates to existing tests