Manage opencode 1.x config via home-manager and isolate opencode2

- Symlink ~/.config/opencode/opencode.json and skills/ from dotfiles
  so opencode 1.x config survives rebuild with zap cleanup
- Track cloud-deploy, cloudflared, github-cli, no-mistakes,
  playwright-cli, and read-tweet skills in repo
- Update opencode2 model to opencode/muse-spark-1.2-contributor-free
- Rotate opencode.json/skills in rebuild.sh alongside existing
  managed paths

rebuild.sh

@@ -40,6 +40,7 @@ managed=(
   "$HOME/.claude/CLAUDE.md"
   "$HOME/.codex/AGENTS.md"
   "$HOME/.config/opencode/AGENTS.md"
+  "$HOME/.config/opencode/opencode.json"
   "$HOME/.config/opencode2/opencode.json"
   "$HOME/.config/opencode2/AGENTS.md"
   "$HOME/.local/bin/oc2"
@@ -60,6 +61,7 @@ for path in \
   "$HOME/.config/wezterm" \
   "$HOME/.config/nvim" \
   "$HOME/.config/herdr" \
+  "$HOME/.config/opencode/skills" \
   "$HOME/.pi/agent/themes" \
   "$HOME/.pi/agent/extensions/calm"
 do