Sketch nodes PIMPL refactor, global dimension settings, OCCT 8 wasm build tooling

[trailcode]

Summary

Tracking branch Trailcode/refactor1: refactor sketch-node internals, add persisted Settings → Sketch → Dimensions controls (line width, arrows, label rendering, visibility), fix permanent node annotation scale, and add OCCT V8.0.0 WebAssembly build scripts plus docs/building-occt.md.

Scope (implemented on branch)

Sketch nodes (src/sketch_nodes.cpp, src/sketch_nodes.h):

• PIMPL-style refactor (Sketch_nodes implementation detail moved behind m_impl).
• Snap / axis-guide behavior preserved; cleaner separation from Sketch.

Dimension style (src/geom.h, src/geom.cpp, src/gui.*, src/sketch.cpp, src/occt_view.*, src/shp_extrude.*):

• Length_dimension_style bundles global dimension display settings.
• apply_length_dimension_style() applies Prs3d_DimensionAspect + AIS Z-layer for labels.
• Settings → Sketch → Dimensions (nested): line width, arrow size/color, text scale, label rendering (0–5; default Z-layer Topmost to avoid grid ghosting), placement, arrow style/orientation, show sketch dimensions.
• Occt_view::refresh_all_length_dimensions() rebuilds dims when settings change.
• Removed non-functional flyout / extension-line settings after OCCT limitations.

Other:

• Permanent node annotation scale fix (gui.permanent_node_anno_scale).
• scripts/build-occt-v8-wasm.ps1 + scripts/build-occt-v8-wasm.cmd — download FreeType, build OCCT V8_0_0 static + GLES2 for Emscripten.
• docs/building-occt.md — Windows prebuilts, wasm build, troubleshooting, wrapper-script patterns.
• usage-settings.md updated for new dimension controls.

Out of scope / follow-ups

• Verify EzyCad wasm links against OCCT 8 install produced by the new script (experimental; README still references 7.9.x manual path).
• Review commits Debug code / WIP — drop or gate debug-only changes before merge.
• Desktop upgrade to OCCT 8.0.0 prebuilts (separate from wasm); retest grid + dimension labels after OCCT 8 grid shader changes.
• Consider typed enum for edge_dim_text_render_mode instead of magic int 0–5.

Test plan

• Settings → Sketch → Dimensions: change each control; confirm live refresh on sketch length dimensions and extrude preview dims.
• Label rendering: try Z-layer Top / Topmost (defaults); confirm no grid bleed-through on labels.
• Show sketch dimensions global toggle; per-sketch list overrides still work.
• Sketch snap: dimension-tool hover, cross-sketch snap, add-node on edge interior (Sketch_test if available).
• Permanent node annotation size slider visible effect on sketch nodes.
• Desktop Release build; open/save settings JSON (edge_dim_* keys).
• (Optional) .\scripts\build-occt-v8-wasm.ps1 completes; emcmake EzyCad with printed OpenCASCADE_DIR.

Links

• Branch: Trailcode/refactor1
• Doc: docs/building-occt.md