PMI: Create and manage the PMI workbench

**User intent:** Access a dedicated workspace for 3D annotation and tolerancing.

**Proposed behavior:**
- The PMI workbench appears in the workbench selector alongside Part, Part Design, TechDraw, etc.
- It offers the creation of a PMI container if a document contains at least one Solid, Surface, Part, Body, or Assembly object
- Activating the workbench shows toolbars organized in sections: Views, Annotations, Visualization, Validation
- The workbench does not modify or interfere with the model geometry. All PMI objects are non-geometric metadata but can have a human-readable 3D representation (also for export).

**Toolbar / menu sections:**
- Views: Add Standard Views, Custom View, Activate View, Edit View, Clipping Plane (still needs to be implemented: [#12187](https://github.com/FreeCAD/FreeCAD/issues/16187))
- Annotations: Datum, Datum System, Dimension, Geometric Tolerance, Note, Leader, Optional: SVG, table (from Spreadsheet), follow up for Surface, Weld,...
- Validation: Query Element, Validate Annotations, Repair Broken References
- Visualization (optional): Toggle Annotations, Filter/Select by Type, Select Linked Geometry, Select Linked Annotations, Stack Frame
- TechDraw Workflow: Derive TechDraw page (not sure if this should be in the PMI WB or TechDraw)

The issue names no files, tests, or entry points; begin by locating the existing workbench registration and PMI-related components. Clarify and split the proposal before implementation, then verify that the workbench selector, eligible-document container, toolbar sections, non-geometric PMI objects, and listed views and validation behaviors are covered.

Written by the indexing model from the issue text.