feat: comprehensive test suite

[sliamh11]

Summary

• 88 tests across 6 test files covering all 8 MCP tools
• Trade execution safety gate (CRITICAL): verifies place_order is disabled by default, returns descriptive error (not crash), validates all order parameters when enabled
• Authentication: auth_status, reauthenticate, gateway-down fallback, competing sessions
• Market data: get_quote warm-up double-call pattern with 1s delay, search_contract results and empty states
• Account & positions: ledger parsing, P&L totals computation, rounding to 2 decimal places, empty state
• Config: Zod validation, required fields, boolean string transforms, URL validation, defaults
• Client: HTTP error handling, num() edge cases (null, string, NaN), tickle heartbeat lifecycle
• Runs in ~200ms total — no real network calls, all mocked

Test plan

• npm test passes: 88/88 tests, ~200ms
• No flaky tests — all deterministic (fake timers for time-dependent tests)
• Test structure mirrors source: tests/config.test.ts, tests/ibkr/client.test.ts, tests/tools/*.test.ts
• Review test coverage for any gaps before merge

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