Organize projects into folders with READMEs and preview renders.

Move the Ring solar siding adapter into its own directory, add repo and
project documentation, and introduce a preview script (OpenSCAD+xvfb or
PyVista fallback) for catalog images.

ring-solar-siding-adapter/README.md

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+# Ring Solar Siding Adapter
+
+![Preview](preview.png)
+
+Parametric adapter plate that sits between a **Ring Solar Charger** (integrated battery-doorbell solar unit) and horizontal beaded vinyl lap siding.
+
+| | |
+|---|---|
+| **Source** | [`ring-solar-siding-adapter.scad`](ring-solar-siding-adapter.scad) |
+| **Footprint** | ~93 × 171 mm (matches the Ring back) |
+| **Units** | Millimeters throughout |
+
+## What it is
+
+- **Front face:** flat — the Ring unit mounts here.
+- **Rear face:** shaped to match siding — bead groove at the top, flat shelf in the middle, curved taper at the bottom.
+
+## What it's for
+
+The Ring's back is flat; siding is not. Without an adapter, you get gaps, uneven pressure, and a poor mount.
+
+This plate:
+
+- Conforms to the siding profile so the rear sits flush against the wall.
+- Receives the siding bead in a semicircular groove near the top.
+- Provides two through-holes aligned with the Ring's house-mount screws — screws pass through Ring → adapter → siding → sheathing.
+
+Typical stack:
+
+```
+Ring Solar Charger
+       ↓ screws
+  Adapter plate  ← this part
+       ↓
+  Vinyl siding
+       ↓
+  Sheathing
+```
+
+## Rear profile (side view, bottom → top)
+
+```
+plate top ─────────────  bead coping groove (receives siding bead)
+            flat rear shelf
+taper start ─────────────  flat_upper_ratio sets this boundary
+            curved taper
+plate bottom ────────────  deepest projection toward front
+```
+
+**Depth convention:** lower depth = toward the wall; higher depth = toward the front (Ring).
+
+## Parameters
+
+### Plate
+
+| Parameter | Meaning |
+|-----------|---------|
+| `plate_width` | Width of the adapter (Ring back width). |
+| `plate_height` | Height of the adapter (Ring back height). |
+| `min_wall_thickness` | Minimum solid depth at the thinnest point (bead groove pinch). Also scales bottom taper reach. |
+| `edge_round` | Rounds front edges via minkowski. Keep `0` while tuning; set ~1 for final print (slower render). |
+
+### Siding profile
+
+| Parameter | Meaning |
+|-----------|---------|
+| `siding_projection` | Nominal max siding depth from wall. Feeds `face_inset_z` via clearance and inset. |
+| `face_inset_depth` | How far the flat upper rear sits in from max projection. |
+| `bead_coping_radius` | Radius of the semicircular bead groove (measured on your siding). |
+| `bead_coping_offset_top` | Distance from plate top to center of the bead groove. |
+| `flat_upper_ratio` | Fraction of plate height (from top down) with a flat rear. Lower = taper starts higher. |
+| `bottom_taper_depth_ratio` | How far the bottom rear reaches toward the front beyond the flat shelf: `min_wall_thickness × this`. Higher = more projection at bottom. |
+| `rear_extension` | Pushes flat rear and taper toward the wall without moving the front face or bead groove vs front/top. Adds overall depth. |
+| `course_pitch` | Bead-to-bead spacing on your siding (~6.5"). Reference for tuning. |
+| `profile_segments` | Curve sampling resolution. Higher = smoother, slower. |
+| `profile_mode` | `curved` = smooth taper; `stepped` = debug fallback with sharp transitions. |
+| `rear_clearance` | Small gap so the part doesn't bind on siding. |
+
+**Common tuning relationships:**
+
+| Goal | Parameter |
+|------|-----------|
+| Move taper start up/down | `flat_upper_ratio` |
+| Bottom taper more/less toward front | `bottom_taper_depth_ratio` |
+| Whole plate deeper front-to-back (bead stays put) | `rear_extension` |
+| Bead groove up/down | `bead_coping_offset_top` |
+| Groove size | `bead_coping_radius` |
+
+### Mounting holes
+
+| Parameter | Meaning |
+|-----------|---------|
+| `mount_hole_offset_top` | Upper hole center distance from plate top. |
+| `mount_hole_offset_bottom` | Lower hole center distance from plate bottom. |
+| `mount_hole_dia` | Hole diameter (4.5 mm for 4 mm Ring screws). |
+| `mount_hole_x` | Horizontal offset from center (`0` = centered). |
+
+### Export
+
+| Parameter | Meaning |
+|-----------|---------|
+| `part_mode` | What to generate (see below). |
+| `profile_strip_width` | Width of the narrow siding fit-test strip. |
+| `front_slice_depth` | Thickness of the front-face test cap (mm). |
+
+**Export modes:**
+
+| Mode | Purpose |
+|------|---------|
+| `full` | Complete adapter with holes — final part. |
+| `profile_strip` | Narrow strip through the rear profile — cheap siding fit test. |
+| `front_slice` | Thin front cap with holes — check width, height, hole placement vs Ring. |
+
+## Suggested workflow
+
+1. **`profile_strip`** — tune siding profile (`flat_upper_ratio`, `bottom_taper_depth_ratio`, `rear_extension`, bead params).
+2. **`front_slice`** — verify Ring hole alignment.
+3. **`full`** — print final plate (PETG/ASA recommended outdoors; PLA OK for tests).
+
+**Print orientation:** front face (Ring side) on the bed, rear profile vertical.
+
+## Related files
+
+| File | Purpose |
+|------|---------|
+| [`ring-solar-siding-adapter.backup.scad`](ring-solar-siding-adapter.backup.scad) | Earlier geometry — flat upper rear + lower taper only, no bead coping groove |
+| `*.stl` | Exported meshes (gitignored; export locally) |
+
+## Regenerate preview
+
+From the repo root:
+
+```bash
+pip install pyvista                    # headless fallback (WSL without display)
+sudo apt install xvfb                  # optional — native OpenSCAD PNG export
+python3 scripts/render-preview.py ring-solar-siding-adapter
+```
+
+Or export a PNG directly from OpenSCAD when a display (or `xvfb-run`) is available:
+
+```bash
+xvfb-run -a openscad --render --viewall --imgsize=1200,900 \
+  -o ring-solar-siding-adapter/preview.png \
+  ring-solar-siding-adapter/ring-solar-siding-adapter.scad
+```