Improve human-readable SCAD specifications and visual design navigation

[brainboxemb]

Context

Migration 011 completed the current-generation SCAD baseline and exposed a
documentation-quality follow-up that should not have expanded the migration
itself.

The numbered documentation structure is useful, but a mechanically correct
30-00-specification.md can still be too terse for a human reader. At the
same time, component-local detailed design documents continue to be generated
with images under prod/bld/design/..., while repository-level design pages
often surface only the source design/design.md authority.

Goal

Improve the shared documentation convention so current-generation SCAD
repositories communicate design intent clearly to people without forcing every
tool/library/project into the same specification template.

Human-readable specification

30-00-specification.md is primarily a human-facing document.

The shared convention should require enough explanation that a reader can
understand:

• why the repository/library/tool exists;
• what problem its abstraction solves;
• why the common/naive alternative is harder to read, maintain or reason about;
• which concepts the user must understand;
• representative usage/behavior at the level appropriate for that repository;
• important non-goals and boundaries.

The exact presentation is repository-specific. Use small code examples,
diagrams, rendered images or concrete scenarios where they improve
understanding rather than imposing identical headings.

Examples of the desired explanatory level:

• Forge: show why raw translate([x, y, z]) forces a reader to decode a vector
  while a semantic move communicates intent directly; explain frame mapping
  separately from simple rotation; show body/remove/keep roles for tagged CSG;
  distinguish Boolean overlap from mechanical clearance in cutters.
• mechint: explain why one shared interface/object definition prevents mating
  geometry and clearance/profile dimensions from drifting independently.
• clamps: explain nominal bore, tension/interference and Boolean overlap as
  separate concepts.
• HUB75: explain mechanical datums/interfaces rather than leaving readers to
  reconstruct them from incidental geometry.

Agent/developer-specific authority may live in AGENTS.md or
20-01-development.md when useful, but it should complement rather than
replace the human explanation.

Generated visual design navigation

Keep component-local design/design.md as source authority.

Where Build publishes a generated readable counterpart with images under
prod/bld/design/..., repository documentation should surface that version
directly as a reading/review surface. A reader should not have to infer the
generated branch/path.

Consider a convention such as:

• source link = edit/authority;
• generated Build link = human visual reading/review;
• repository 40-00-design.md or its index exposes both where available.

Suggested work

1. update the shared repository/SCAD documentation conventions;
2. decide whether any agent-specific guidance belongs in the shared AGENTS or
   development-manual convention;
3. audit the current-generation SCAD repositories for specification depth;
4. improve each specification according to its own domain/problem, using code
   examples or visuals where useful;
5. audit 40-00-design.md navigation to generated visual design documents;
6. qualify the convention on representative repositories before a broader
   rollout.

Boundary

This is follow-up documentation work after Migration 011. It does not reopen
the already-qualified Migration-011 owner or consumer releases and should not be
treated as a reason to manufacture new releases unless a later change actually
needs one.