feat: add mock investigation mode for UI development
- lib/mocks/confidence-engine/mock-client.js: self-contained ESM interceptor with 6 inline turn fixtures, no external deps or require() calls
- components/scenario-form.jsx: MOCK_ENABLED compile-time boolean, useMockGlobals() hook injects window.__MOCK_* globals at runtime, ternary dispatch to mockFetch
- .env.example: NEXT_PUBLIC_CONFIDENCE_ENGINE_MOCKS, MOCK_DELAY, MOCK_SCENARIO env vars
- docs/v0.7-ui-mock-mode.md: setup, scenarios (default/complete/error), architecture, safety rules, fixture schema
robbond
97a4847770