Enhance multi-device support with presets and angled gussets

[rwb5510]

Summary

Combines the dual-sleeve fork with the keystone jack PR and adds two new features on top: angled support gussets for heavy devices, and a device preset table so the most common rack-mounted gear can be selected by name.

Going from the original single-opening generator to this version:

	Original	This PR
Openings per faceplate	1	1–4 (section_count)
Keystone jacks	no	per-section, side-selectable
Support gussets for heavy loads	no	per-section, auto-clamped
Device sizing	manual (W/H/D)	preset dropdown or Custom
Front-panel cutout collision checks	—	rail column + wire holes

What changed

Multi-section layout (extends #20 by @cjolivier01)

• section_count parameter (1–4). The original dual-sleeve branch hard-coded two sections; this generalizes to N with a unified iteration model.
• Each section has its own width / height / depth / x_offset / y_offset plus independent feature flags.
• Rack holes, air holes, zip-tie features, and wire holes all iterate per section; disabled sections are skipped entirely.
• Shared rack-hole extrusion depth uses max(section_depth) so the slots still punch through the deepest sleeve.

Keystone jack cutouts (extends #21)

• Per-section sectionN_keystone toggle, count (1–6), and side-of-opening selector (left/right of that specific opening).
• Standard 14.94 × 16.51 mm cutouts with a configurable tolerance and jack-to-jack spacing.
• Cutout depth is front_thickness + 2·tolerance — punches only the faceplate, not the sleeve.
• Automatic clearance from two obstacles:
  • Front wire holes (when front_wire_holes is enabled): keystones are pushed outward by wire_diameter × 0.7 so the circles don't clip the jack bezel.
  • Rack-rail slot columns: any jack that would land within slot_len/2 + support_rail_margin of the rails is skipped with an echo warning instead of cutting into the mounting slot.

Angled support gussets (new)

• Per-section sectionN_support toggle. When enabled, renders triangular prisms on both outer walls of the sleeve, attaching chassis side to faceplate.
• Gusset is outside the sleeve cavity so it never blocks device insertion.
• Two global sizing params: support_width_requested (how far along the faceplate) and support_depth_requested (how far back along the sleeve).
• The width is clamped per side, per section to the nearest obstacle: either an adjacent section's chassis wall or the rack-rail column, minus support_rail_margin. If the available gutter drops below support_min_width, that side is skipped with an echo warning.
• Rationale: a ~1.2 kg Mac Mini or ~1.3 kg OptiPlex Micro cantilevered on a 3 mm PLA faceplate puts sustained bending load on the sleeve-to-faceplate joint. PLA creeps under sustained load at room temperature; a gusset dramatically raises the joint's moment of inertia and reduces long-term deformation.

Device presets (new)

• sectionN_device dropdown with ~25 preloaded sizes (Firewalla, UniFi, Intel/Dell/HP/Lenovo micro PCs, Mac Mini, Synology DS-series, etc).
• Preset dimensions sourced from the MakerWorld 10-inch Mini Rack Generator project page: https://makerworld.com/en/models/1765102-10-inch-mini-rack-generator
• Selecting a preset overrides the section's custom width/height/depth. Choosing Custom uses the manual values, preserving the original workflow.
• An echo warning fires on preview if a chosen preset is taller than rack_height (e.g. picking a Mac Mini in a 1U config).

Parameter file organization

• Grouped with OpenSCAD customizer section headers (/* [Section 1] */ etc.) so the customizer groups parameters by section and feature.

Credits

• Dual-sleeve implementation: @cjolivier01, PR Added dual sleeved version #20 ("Added dual sleeved version").
• Keystone jack feature: PR add option for keystone jacks #21 (this author).
• Preset device dimensions table: taken from the MakerWorld "10-inch Mini Rack Generator" project (https://makerworld.com/en/models/1765102-10-inch-mini-rack-generator).
• Support gusset feature, collision clamping, N-section generalization, preset dropdown, warnings: this PR.

Testing notes

• Render 1U single-section with preset = UniFi Security Gateway, verify matches original design.
• Render 1U two-section with both Firewalla Purple SE, keystones set to center layout (§1 right, §2 left).
• Render 2U single-section with M4 Mac Mini preset and support = true.
• Toggle front_wire_holes with keystones enabled on both sides; check no bezel-to-wire-hole overlap in preview.
• Four-section layout with offsets chosen to leave < 3 mm gutter on one side; confirm support gets skipped (check console for warning).
• Verify customizer dropdown populates with all presets on OpenSCAD 2021.01+.