test: add comprehensive test coverage for Passmark framework

[chemicoholic21]

Addresses Issue #2 by expanding test coverage across all priority areas:

PRIORITY 1 — Placeholder Resolution (43 tests)

• {{run.*}} placeholder generation and validation
• {{global.*}} placeholder persistence across executionIds
• {{data.*}} placeholder resolution from Redis
• {{email.*}} lazy resolution with provider integration
• Malformed placeholder handling and error cases

PRIORITY 2 — Caching Logic (31 tests)

• Cache HIT: uses cached actions without AI calls
• Cache MISS: AI execution and Redis storage
• bypassCache flag at step and runSteps level
• Playwright retry detection bypasses cache
• Auto-healing on cached action failures
• Cache key scoping by userFlow + description
• All cached action types (click, fill, hover, etc.)

PRIORITY 3 — Assertion Consensus (20 tests)

• Both models agree TRUE → assertion passes
• Both models agree FALSE → assertion fails
• Models disagree → arbiter makes final call
• Arbiter agreement with Claude or Gemini
• API error handling with retry logic
• Effort level affects thinking mode
• Custom images support

PRIORITY 4 — configure() and Model Slots (45 tests)

• Model override for all 7 model slots
• configure() merges settings across calls
• Gateway switching (vercel, openrouter, cloudflare, none)
• resolveAI() precedence: step > call > global > default
• CUA model lock validation
• Clear error messages for misconfigurations

PRIORITY 5 — runSteps() Failure Modes (25 tests)

• Step failures throw descriptive StepExecutionError
• waitUntil timeout handling
• Empty steps array gracefully handled
• undefined/null page handling
• Script step validation and failures
• CUA mode error handling
• Assertion skipping on step failure
• Data extraction failures
• Redis unavailability fallback

Test Infrastructure

• All tests use proper vi.mock() patterns
• In-memory Redis mock (Map<string, string>)
• AI SDK mocks prevent real API calls
• Playwright page stubs for automation
• Comprehensive edge case coverage

All 298 tests passing with full isolation.