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/apps/visualizer/.oxlintrc.json

@@ -0,0 +1,18 @@
+{
+  "$schema": "./node_modules/oxlint/configuration_schema.json",
+  "plugins": ["typescript", "unicorn", "oxc"],
+  "categories": {
+    "correctness": "error",
+    "suspicious": "warn",
+    "perf": "warn"
+  },
+  "env": {
+    "browser": true,
+    "es2024": true
+  },
+  "rules": {
+    "no-console": "off",
+    "typescript/no-explicit-any": "warn"
+  },
+  "ignorePatterns": ["dist/**", "node_modules/**"]
+}