Improve rendering hot paths and simplify runtime validation

[devmobasa]

Summary

This PR delivers ten focused performance and maintainability improvements:

• Share embedded image payloads and use identity-based render caching
• Render packed pressure samples without intermediate allocations
• Cache window-snap display geometry
• Borrow large board-picker layouts in hot paths
• Borrow large region-capture visual structures
• Split complex arrow and step-marker rendering into focused helpers
• Separate CLI validation by concern
• Centralize preset validation and cover every supported slot
• Defer fallback lookups until they are needed
• Reuse allocations during session and output transitions

The improvement plan was reviewed twice. Broad lint churn, arbitrary file splitting, and lower-impact telemetry cleanup were excluded in favor of measured hot-path work and cohesive refactoring.

Each improvement is contained in a separate commit.

Validation

• Full ./tools/lint-and-test.sh passed
• Formatting and strict Clippy passed
• All-feature and no-default-feature configurations passed
• Core, configurator, integration, UI, and documentation tests passed
• Packaging, source-coverage, and repository audits passed
• git diff --check passed