- Replace Liquid/Jinja template syntax ({{ arguments }}, {% if %}) with
  $ARGUMENTS in solve.md and solved.md — OpenCode command templates use
  shell-style variable substitution, not Jinja
- Remove invalid `write: deny` from nexus-planner.md (edit: deny already
  covers write/apply_patch/multiedit per OpenCode permission model)
- Build script now targets darwin (arm64, x64) and win32 (x64) only;
  no Linux builds needed for Nexus distribution
- Binary output renamed from opencode-* to nexus-* to match CLI name
- Release packaging simplified to zip-only (no tar.gz, no linux paths)

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>