test(e2e): add ChapterView flows + stabilize runner

[anantham]

Summary

Adds Playwright E2E coverage for ChapterView (large import/diff navigation + illustration rendering) and hardens the Playwright runner to avoid port collisions.

Changes

• playwright.config.ts: run a dedicated dev server on 127.0.0.1:5177, set baseURL accordingly, disable auto-opening HTML report.
• tests/e2e/chapterview-large.spec.ts: import a large session fixture and verify diff navigation.
• tests/e2e/chapterview-media.spec.ts: verify persisted suggestedIllustrations.generatedImage.imageData renders as an <img> and the audio generate button is enabled.
• tests/e2e/helpers/sessionHarness.ts: shared helpers (fresh install + session import).
• tests/e2e/{diagnostic,debug-console}.spec.ts: gate behind LF_E2E_DIAGNOSTICS=1.
• .gitignore: ignore playwright-report/ and test-results/; remove tracked playwright-report/index.html.
• docs/E2E-TESTING.md: document dedicated port usage.

Testing

• npm run test:e2e

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Project	Deployment	Review	Updated (UTC)
lexicon-forge	Ready	Preview, Comment	Dec 26, 2025 8:11pm