feat: add JoyCode install target

docs/JOYCODE-GUIDE.md

@@ -0,0 +1,55 @@
+# JoyCode Adapter Guide
+
+JoyCode can consume ECC through the selective installer. The adapter installs shared ECC commands, agents, skills, and flattened rules into a project-local `.joycode/` directory.
+
+## Install
+
+Preview the install plan:
+
+```bash
+node scripts/install-plan.js --target joycode --profile full
+```
+
+Apply it to the current project:
+
+```bash
+node scripts/install-apply.js --target joycode --profile full
+```
+
+For a smaller install, select modules explicitly:
+
+```bash
+node scripts/install-apply.js --target joycode --modules rules-core,commands-core,workflow-quality
+```
+
+## Layout
+
+The project adapter writes managed files under:
+
+```text
+.joycode/
+  agents/
+  commands/
+  rules/
+  skills/
+  mcp-configs/
+  scripts/
+  ecc-install-state.json
+```
+
+Rules are flattened into namespaced filenames so a JoyCode project does not receive nested rule directories such as `rules/common/coding-style.md`. Commands, agents, and skills keep the same structure they use elsewhere in ECC.
+The full profile also includes shared MCP and setup helper files that other ECC project-local adapters use.
+
+## Uninstall
+
+Use ECC's managed uninstall path instead of deleting files by hand:
+
+```bash
+node scripts/uninstall.js --target joycode
+```
+
+The uninstall command reads `.joycode/ecc-install-state.json` and removes only files that ECC installed. User-created JoyCode files are preserved.
+
+## Source PR
+
+This adapter salvages the useful project-local JoyCode intent from stale PR #1429 while replacing the standalone shell installer with ECC's current install-state and uninstall machinery.