feat(scadm): dynamic OpenSCAD version resolution

[Copilot]

📦 What

Replace hardcoded nightly version constants with dynamic "latest" resolution. Unify the two separate Windows/Linux nightly constants (identical since ~2026.01.03) into a single config-driven approach.

• New resolver.py module: scrapes OpenSCAD snapshots page (nightly) or GitHub releases API (stable), with local caching in bin/openscad/.resolved-version
• New openscad config section in scadm.json with type (nightly/stable) and version (latest/pinned)
• New --info flag on scadm install to show configured, resolved, and installed versions
• Removed --stable CLI flag (breaking) — type now comes from config
• Removed OPENSCAD_NIGHTLY_VERSION_WINDOWS, OPENSCAD_NIGHTLY_VERSION_LINUX, OPENSCAD_STABLE_VERSION from constants.py
• Updated Renovate: replaced 3 constants.py custom managers with 1 scadm.json version manager
• 26 new tests (18 resolver + 8 installer config)

💡 Why

Renovate was creating separate PRs for Windows and Linux nightly versions that have been identical since 2026.01. The constants-in-code approach required a code change + release for every version bump. With "version": "latest", scadm resolves dynamically — no code changes needed. Pinned versions still work for reproducibility and Renovate tracking.

🔧 How

Backward compatible — missing openscad section defaults to {"type": "nightly", "version": "latest"}.

{
  "openscad": {
    "type": "nightly",
    "version": "latest"
  },
  "dependencies": [...]
}

Pin a specific version to opt out of dynamic resolution:

{
  "openscad": {
    "type": "nightly",
    "version": "2026.03.28"
  }
}

scadm install           # resolves + installs latest nightly
scadm install --force   # bypasses resolved-version cache
scadm install --info    # shows configured/resolved/installed versions

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• files.openscad.org
  • Triggering command: .venv/bin/scadm .venv/bin/scadm install (dns block)
  • Triggering command: /home/REDACTED/.local/bin/scadm scadm install --info (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)