security: pin Jira attachment download to the configured Jira host

[Copilot]

downloadJiraAttachments sent the Jira Basic-auth header (email:PAT) to attachment.content — a URL taken verbatim from attacker-influenceable API metadata — with no host validation, allowing PAT exfiltration to an arbitrary host and SSRF against internal endpoints. GitHub and ADO providers already pin their hosts; Jira did not.

Changes

• provider-jira.ts: Added assertSameJiraHost(), invoked per attachment before any auth header is sent. It rejects the content URL unless it parses cleanly, uses https:, and its host matches the configured JIRA_BASE_URL host.
• provider-jira.test.ts (new): Regression tests mocking requestJson/requestBinary — off-host and non-HTTPS content URLs are rejected and assert requestBinary is never called; a valid on-host HTTPS URL is downloaded.

for (const attachment of images) {
  assertSameJiraHost(attachment.content); // throws before requestBinary sends the PAT
  const safeName = basename(attachment.filename);
  const outputPath = join(outputDir, safeName);
  const bytesWritten = await requestBinary(attachment.content, headers, outputPath);
  ...
}

Notes

• Enforces https: in addition to host match, closing credential-over-cleartext downgrades.
• Aligns with the allowlist mandate in skills/security/SKILL.md and the existing GitHub/ADO host-pinning pattern.