Security hardening: CI permissions/pinning, webview/hover, policy

[magnesj]

Defense-in-depth hardening pass. No high-severity vulnerability was found; these changes close latent gaps and tighten the supply-chain posture.

CI workflow

• Add top-level permissions: contents: read. The package job still elevates to contents: write for the release upload.
• Pin every action to a full commit SHA (with # v<n> trailing comment):
  • actions/checkout, actions/setup-python, actions/setup-node, actions/upload-artifact, actions/download-artifact
  • softprops/action-gh-release (third-party — highest-value pin)
• Pin @vscode/vsce@3.9.1 (build + publish) and ovsx@0.10.12 so the publish step holding VSCE_PAT no longer auto-installs latest at runtime.

Extension (vscode-extension/src/extension.ts)

• escHtml also escapes single quotes (' → ') — closes a latent footgun if any future attribute is single-quoted.
• The <td>${p.index}</td> cell now goes through escHtml to match the attribute usage on the same line.
• DocsViewProvider sets localResourceRoots: []. The webview renders only inline content and never needs filesystem access.
• Drop md.isTrusted from buildKeywordHover and buildParameterHover. supportHtml is kept where the inline <span> notices need it. isTrusted would additionally permit command: link execution, which these hovers never use.

New files

• SECURITY.md — supported-versions statement and private vulnerability reporting via GitHub Security Advisories.
• .github/dependabot.yml — weekly updates for npm (vscode-extension/), pip (scripts/), and github-actions (/). Keeps the new SHA pins fresh.

Verification

• tsc -p ./ — compiles clean.
• jest — 189/189 tests pass.
• YAML files parse.