Document and apply tabular C++ layout / blank-line rhythm

[trailcode]

Summary

Codify hand-aligned tabular layout (with local // clang-format off/on), blank-line vertical rhythm, and happy-path-first control flow in docs/ezycad_code_style.md, and apply those presentation rules to a few src/ files. No intended behavior changes.

Problem

• Hand-aligned key/value tables and one-line switch cases were used in places but not spelled out in the style guide.
• Agents and contributors defaulted to file-wide clang-format off or packed UI/helper beats that did not match the preferred paragraph rhythm.

Scope

Documentation:

• docs/ezycad_code_style.md — Tabular layout (including short parallel switch cases), vertical rhythm (blank lines), control-flow polarity (happy-path first).

Code (presentation only):

• src/gui_settings.cpp — JSON/assignment tables wrapped in local clang-format off/on; blank-line rhythm tweaks.
• src/shp_cross_section.cpp — one-line-per-case switch tables; minor blank-line cleanup.
• Nearby shape/sketch helpers — blank lines before returns / between logical beats (nitpick cleanup).

Acceptance criteria

• Style guide documents tabular layout, blank-line rhythm, and happy-path-first preference.
• gui_settings.cpp / shp_cross_section.cpp use local clang-format off/on around tables only (not whole TU).
• Review confirms no functional/behavior changes.
• CI green on the PR branch.

Related

• Branch: Trailcode/nitpick