Shape List Zoom to, shaft-align mode rename, and third_party IDE filters

[trailcode]

Summary

• Shape List Zoom to (name and M menus) via Occt_view::fit_shapes_in_view — frames a solid or group descendant solids while keeping camera orientation.
• Rename Mode::Shape_cyl_align → Mode::Shape_shaft_align (hotkey id mode.cyl_align / Shp_cyl_align unchanged).
• Nest imgui / TextEditor / tinyfiledialogs under third_party IDE filters in EzyCad_lib (CMake source_group).
• Sync gui.md Align shafts Options / Tab / Enter / dist-edit routing; usage.md + CHANGELOG for Zoom to.

Test plan

• Build Release EzyCad
• Shape List solid: right-click name / M → Zoom to frames solid, orientation unchanged
• Group with solids: Zoom to frames all descendants; empty group item disabled
• Align shafts (J): Options Flip / Clock rotation still work after mode rename
• Reconfigure CMake, reload build/EzyCad.sln: EzyCad_lib → third_party/{imgui,ImGuiColorTextEdit,tinyfiledialogs}
• Spot-check docs/usage.md Shape List, src/doc/gui.md Options/keyboard, CHANGELOG

Closes #248

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Note

Low Risk
Localized UI/view framing and a mechanical mode enum rename with no hotkey or behavior changes; CMake changes affect IDE layout only.

Overview
Adds Shape List Zoom to on solid/group name and M context menus, calling new Occt_view::fit_shapes_in_view to frame one solid or all descendant solids with padding while keeping the current camera orientation (disabled for empty groups and solids without geometry).

Renames Mode::Shape_cyl_align → Mode::Shape_shaft_align across GUI/OCCT mode dispatch (toolbar, Tab/Enter routing, Options options_shape_shaft_align_mode_); mode.cyl_align / Shp_cyl_align stay unchanged.

CMake nests imgui, TextEditor, and tinyfiledialogs under a third_party Solution Explorer tree for EzyCad_lib via source_group(TREE …) and header-only target_sources.

User and developer docs (CHANGELOG, usage.md, gui.md, shape.md) and agent drafts are updated; remaining diff is mostly formatting.

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