chore(ci): remove LLM summary generation from vulnerability triage

Replace the Claude analysis step in the vulnerability-triage workflow with
deterministic jq/curl scripting. Findings are now built directly from the
normalized Trivy, Dependabot, and CodeQL scan files (dedup by pre-computed
id, CodeQL grouped by rule, templated titles/descriptions), and existing
Linear issues are matched via GraphQL. No LLM is used anywhere.

Drops the ANTHROPIC_API_KEY secret from the reusable workflow (no callers
pass it).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: brendan-kellam