Add sssf skill, installable via the skills CLI

Port the sssf skill from ~/.agents/skills/sssf into this repo so it can be
distributed and installed with the skills CLI (skills add INDigitalStudio/skills
--skill sssf).

- Copy the skill (SKILL.md, cookbooks, references, scripts, templates, and the
  visualizer app source) into sssf/.
- Gitignore build/runtime artifacts: the visualizer's node_modules/ and dist/,
  Python bytecode, and the machine-specific repos.json.
- Make the skill location-independent: install.py now stamps the skill's real
  path into the stamped justfile's skill_dir (replacing the hardcoded
  ~/.agents/skills/sssf), so 'just obs' finds the visualizer wherever the CLI
  installed the skill.
- Update cookbooks to use <skill>/scripts/... instead of the hardcoded path,
  and document the skills CLI install command.
- Update the repo README with install instructions.

README.md

@@ -3,3 +3,26 @@
 General folder for the skills we create or modify.
 
 This repository holds the skills we develop and maintain. Each skill lives in its own directory with a `SKILL.md` describing its purpose and usage.
+
+## Installing a skill
+
+Skills are distributed from this repo and installed with the [skills CLI](https://github.com/vercel-labs/skills):
+
+```bash
+# list what's available
+skills add INDigitalStudio/skills --list
+
+# install one skill (e.g. sssf) globally
+skills add INDigitalStudio/skills --skill sssf -g -y
+
+# install every skill in the repo
+skills add INDigitalStudio/skills --all -g -y
+```
+
+The CLI discovers each skill by its `SKILL.md` (which must declare `name` and `description` frontmatter) and copies the whole skill directory into your agent's skills folder.
+
+## Skills
+
+### sssf
+
+Super Simple Software Factory — deploy and operate repeatable agents+code workflows (ADWs) in any codebase. See [`sssf/SKILL.md`](sssf/SKILL.md) and its `cookbooks/` for usage.