feat: CRT phosphor shader engine and retro themes

[chernistry]

Summary

• Adds CRTShader class in src/bernstein/tui/crt_shader.py that transforms Rich Text to simulate a 1987 CRT monitor with scanline dimming, phosphor bloom, chromatic aberration, and monochrome palette mapping (amber/green/cool white)
• Adds three retro CRT themes (RETRO_AMBER, RETRO_GREEN, RETRO_COOL) to the theme system in themes.py and integrates them into the theme cycle
• Includes 23 unit tests covering all shader effects, mode cycling, edge cases, and precomputed LUT correctness

Test plan

• All 23 new CRT shader tests pass (uv run pytest tests/unit/test_crt_shader.py -x -q)
• All existing theme tests pass with updated cycle order (uv run pytest tests/unit/test_tui_themes.py -x -q)
• Ruff lint clean
• Pyright strict mode clean
• Visual verification deferred to post-integration (library module, no UI hookup yet)

🤖 Generated with Claude Code

[github-actions]

AI Review (GitHub Models)

Summary

The pull request introduces a CRT phosphor shader engine and retro themes for the Bernstein CLI orchestrator. This addition enhances user experience by providing visual customization options, appealing to users interested in retro aesthetics.

Risk Assessment

Medium - While the changes focus on non-core functionality (visual themes), inefficient implementations or security vulnerabilities within the shader engine could impact performance or user security.

Actionable Recommendations

• Code Review: Conduct a thorough review of the shader implementation for performance issues, especially on lower-spec machines.
• Security Audit: Verify that the shader code does not unintentionally expose vulnerabilities, particularly with input handling.
• Documentation Update: Ensure that documentation includes information about the new features and how to utilize them effectively.
• Testing: Add unit and integration tests covering the new functionality to ensure stability.
• Deprecation Planning: Consider the impact on existing themes and document any deprecations or breaking changes introduced.

[github-actions]

CI Summary

Check	Result
Repo hygiene	✅ success
Lint	✅ success
Type check	✅ success
Tests	❌ failure
Spelling	✅ success
Dead code	✅ success
Workflow lint	✅ success
Dist size	✅ success
SonarCloud	⏭️ skipped

Coverage and detailed reports are available via Codecov and the Checks tab.

[sonarqubecloud]

Quality Gate failed

Failed conditions
C Reliability Rating on New Code (required ≥ A)

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