Document tabular layout and apply presentation nitpicks

[trailcode]

Summary

• Document hand-aligned tabular C++ layout (including short one-line switch cases), blank-line vertical rhythm, and happy-path-first control flow in docs/ezycad_code_style.md.
• Apply those presentation rules in gui_settings.cpp and shp_cross_section.cpp (local // clang-format off/on around tables only), plus light blank-line cleanup in nearby shape/sketch files.
• No intended runtime behavior changes.

Closes #229

Test plan

• Spot-check docs/ezycad_code_style.md Tabular layout / Vertical rhythm / Control flow polarity sections.
• Confirm gui_settings.cpp and shp_cross_section.cpp keep clang-format off/on tight to tables (not file-wide).
• Build / CI green (presentation-only; no feature tests expected).
• Quick sanity: Settings dialog still loads/saves; cross-section tool still previews/clips.

Notes

• Branch is formatting/style nitpick only (Trailcode/nitpick).

---

Note

Low Risk
Mostly documentation and formatting; the Defaults-button and cross-section message refactors are equivalent control flow but worth a quick sanity check in Settings and cross-section clip UX.

Overview
docs/ezycad_code_style.md adds guidance for hand-aligned tabular blocks (JSON keys, assignments, one-line switch cases) with tight // clang-format off/on, plus vertical rhythm (blank lines around ImGui chains, lambdas, returns) and happy-path-first if/else.

gui_settings.cpp and shp_cross_section.cpp are the main code updates: column-aligned settings JSON builders/parsers and compact switch tables; many blank lines before ImGui::SameLine / help tooltips and in the Settings UI. Smaller touch-ups in shp_create, shp_move, shp_rotate, fuse/cut/extrude, skt.cpp, etc. (spacing, polarity). shp_cross_section.h drops an unused #include <cstddef>.

The Settings Defaults button is refactored to if (!content.empty()) { … } else show_message(...) (same outcomes). Clip-message and similar branches use success-first ordering; logic is unchanged per the PR intent.

^{Reviewed by Cursor Bugbot for commit f4a1900. Bugbot is set up for automated code reviews on this repo. Configure here.}