Refactor clear_all resets and file-local helper layout

[trailcode]

Summary

Tighten reset and helper conventions: extend clear_all for enums/aggregates, convert multi-field reset sites to clear_all, and align anonymous-namespace helpers with trailing _ names (declare near top / define at file bottom). Update the style guide so agents and humans share the same rule.

Problem

• Multi-field reset blocks were hand-rolled and easy to leave incomplete.
• clear_all already covered optionals/arithmetic/handles but not enums or plain aggregates.
• File-local helpers were inconsistently named/placed vs private methods (name_) and the documented reader-first .cpp layout.

Implemented scope

Code:

• src/utl.h / src/utl.inl: document and support enum + aggregate reset via T{}.
• Shape/sketch/GUI reset call sites: shp_cyl_align, shp_move, shp_extrude, shp_cross_section, shp_rotate, skt_*, gui.cpp, hover clear in gui_occt_view.
• File-local helpers: trailing _, forward decls + bottom defs across GUI (gui_add, gui_settings, gui.cpp, gui_occt_view), shape/sketch (shp_*, skt_*), utilities (utl_*), and main.cpp.
• ImGui add-primitive dialogs: shared table_row_input_double_.

Documentation:

• docs/ezycad_code_style.md — private methods and file-local helpers share trailing _; helper organization wording.
• src/doc/utility.md — clear_all coverage.

Out of scope: scr_*.cpp Lua/Python bindings (different style; optional follow-up).

Acceptance criteria

• clear_all resets enums and aggregates safely.
• Touched reset sites use clear_all where sequencing allows.
• Touched file-local helpers use name_ with bottom definitions.
• Style / utility docs match behavior.
• Release build and EzyCad_tests (127) pass.

Notes

• AIS erase-then-Nullify sequences left explicit where order matters.