style: adopt lean rectangular design and en dash typography

[BotshareAI]

Summary

• replace all 336 em dashes across the public documentation with grammatically correct spaced en dashes
• move the full site toward a lean, engineered visual language with near-square corners
• flatten cards, buttons, banners, labels, tables, and navigation elements
• remove floating hover movement and reduce decorative shadows while preserving hierarchy
• remove redundant navigation status icons while retaining visible page-level development banners
• render breadcrumbs as a single horizontal folder-style path
• consolidate Architecture, Repositories, Mobile Platform, Upper Body, Interfaces, and Communication under canonical /reference/ URLs
• redirect legacy URLs and the obsolete technical getting-started router
• clarify that repositories own exact versions and contracts while this site provides the complete learning layer
• correct obsolete /learn/... routes on Start here

Typography decision

The site now uses the spaced en dash (–) for parenthetical breaks. This is shorter and visually lighter than an em dash while remaining grammatically standard in British and international publishing styles.

Validation

• git diff --check
• zero remaining —, —, or page-level navigation status: metadata
• zero development-status icons in the generated Build navigation
• legacy Architecture output verified as a redirect to /reference/architecture/
• python -m mkdocs build --strict