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.

sssf/templates/adws/adw_modules/prompts.py

@@ -0,0 +1,21 @@
+"""Prompt rendering: load system/user refs from config, replace {{placeholders}}."""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+
+def render(template_path: str | Path, variables: dict[str, str]) -> str:
+    text = Path(template_path).read_text()
+    for key, value in variables.items():
+        text = text.replace("{{" + key + "}}", value)
+    return text
+
+
+def save(directory: str | Path, name: str, content: str) -> Path:
+    """Save the exact prompt sent, before execution — the audit copy."""
+    directory = Path(directory)
+    directory.mkdir(parents=True, exist_ok=True)
+    path = directory / name
+    path.write_text(content)
+    return path