feat: test suite (272 tests), persistence layer, retry logic, bug fixes

[arc-web]

What's in this PR

Test Suite (4 files, 272 tests, vitest)

• mogul.test.ts (48 tests): Phase routing, fallback tiers, provider health, budget enforcement, retry logic, delegation, persistence integration
• landlord.test.ts (39 tests): Spike detection, anomaly patterns (rapid-fire, thrashing, output explosion), severity levels, key compromise detection
• portfolio.test.ts (171 tests): Validates every field on all 16 models, tier assignments, cost sanity, strength coverage
• persistence.test.ts (14 tests): JSON file roundtrip, memory adapter, error recovery

Persistence Layer (src/persistence.ts)

• PersistenceAdapter interface with save() and load()
• JsonFilePersistence - file-based JSON storage
• MemoryPersistence - in-memory adapter for testing
• Auto-loads on startup, auto-saves after each complete()

Retry Logic

• Configurable retryConfig: { maxRetries, baseDelayMs, multiplier }
• Exponential backoff before marking providers degraded
• Default: 2 retries, 1s base, 2x multiplier

Bug Fixes

• Global mutable state (MARKET_SENTIMENT, PORTFOLIO_LEDGER) moved to instance-scoped
• TypeScript errors in examples/landlord.ts fixed
• Duplicate model ID in local portfolio fixed
• Added .gitignore

All 272 tests pass. TypeScript compiles clean. Build succeeds.