Initial commit of SSVC-AI decision point evaluation skill

[sei-renae]

Changes

• Adds a reusable eval-against-decision_point base skill that defines the shared SSVC evaluation workflow, confidence thresholding, dependency handling, and JSON output schema.
• Adds a technical-impact SSVC skill for evaluating the Technical Impact decision point against vulnerability reports.
• Adds OpenCode configuration for the ssvc-docs reference so skills can fetch canonical SSVC docs and source files at runtime.

additional info for local testing

I have in my global .config/opencode/.opencode.jsonc:

"permission": {
    "webfetch": "ask",
    "bash": {
      "pip install*": "ask",
      "pip3 install*": "ask",
      "npm install*": "ask",
      "brew install*": "ask",
      "brew upgrade*": "ask",
      "curl*": "ask",
      "wget*": "ask",
      "*": "ask"
    }
  }

and in my global .config/opencode/instructions.md:

# Global Coding Instructions

## Python

- All Python code must be run inside a virtual environment (venv).
- Before running any `python` or `python3` command, ensure a venv is active or create one first.
- Never install Python packages globally (no `pip install` or `pip3 install` outside a venv, and never use `--break-system-packages`).
- To set up a venv for a project:
  ```bash
  python3 -m venv .venv
  source .venv/bin/activate
  pip install <package>```