hardware/mechanical/ is empty — no CAD for any form factor #6

Observation

$ ls hardware/mechanical/
README.md

The directory is referenced from docs/design/assembly_guide.md and README.md as the canonical location for mechanical CAD, but it currently holds only a README. No STEP, STL, IGES, or FreeCAD files exist for:

• CanSat cylindrical housing (Ø68 × 80 mm for cansat_standard, Ø66 × 115 for cansat_minimal, Ø68 × 115 for cansat_advanced).
• CubeSat frames for any of the six registered sizes (1U / 1.5U / 2U / 3U / 6U / 12U).
• Deployables (antennas, solar wings for 6U / 12U).

Why it matters

• Teams following docs/ops/*.md can't 3D-print or CNC-machine the housing from the repo alone — they have to design the mechanics from scratch.
• docs/budgets/mass_budget.md talks about "3U Primary Structure (ISIS 3U Structure Kit) 280 g" as a BOM line item without a matching CAD export.
• The registered envelope in flight-software/core/form_factors.py is authoritative for dimensions; a STEP file that matches those numbers would close the loop.

Definition of done

Minimum for cansat_standard (most common CanSat competition kit):

• hardware/mechanical/cansat_standard/housing.step — Ø68 × 80 mm with inner Ø64, end caps, 4 × M2 PCB mount posts.
• hardware/mechanical/cansat_standard/housing.stl — ready-to-print.
• Cross-referenced from docs/design/assembly_guide.md and docs/ops/cansat_standard.md.

Stretch: same for cansat_minimal, cansat_advanced, and cubesat_3u.

Not blocking v1.x; closes a long-standing gap between the software envelope registry and the physical build chain.