feat(stem): add configurable flying stem generator

[richardsolomou]

Problem

BaseKit could generate miniature bases and holders, but not the printable stems needed to mount flying miniatures. Users had to design or source compatible stems separately.

Changes

• Add a dedicated Flying Stems generator at /stems.
• Support 15, 20, 30, and 35 mm body heights.
• Add configurable body diameter and peg or ball-joint miniature connections.
• Include stem settings in persisted workspace state with migrations for existing workspaces.
• Add stem-specific preview, export naming, dimensions, analytics, and title-block details.
• Add geometry, workspace, and end-to-end tests.
• Document flying stems in the README.

Risk

Low. The new generator is isolated from existing base and holder geometry. Shared routing, workspace migration, preview framing, and export handling are the main affected paths.

Verification

• Added unit tests for stem dimensions, solid geometry, connection variants, vertex welding, and validation.
• Added workspace migration tests for new stem settings.
• Added an end-to-end test covering stem navigation, dimensions, peg settings, and ball-joint settings.

Checklist

• Tests cover new or changed behavior where practical.
• Geometry changes are checked against a real export, not just the preview.
• User-facing behavior is documented in the README.

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	basekit	8ab0a9c	Commit Preview URL Branch Preview URL	Sep 05 2026, 11:08 PM