chore: remove the Claude Code GitHub Actions workflow #2102

Problem

.github/workflows/claude.yml runs the @claude mention-triggered agent on issue comments, PR review comments, PR reviews, and issue open/assign. Every one of those triggers now produces an Actions run that sits waiting for approval, so the workflow list fills with pending runs a maintainer has to clear by hand — for a capability we no longer rely on.

We use Copilot for PR review now, so the workflow no longer earns the maintenance it costs. Beyond the approval noise it also carries real surface area: it is the only job holding ANTHROPIC_API_KEY, it grants a tool-enabled agent Bash, and it needs a fork gate, SHA-pinned actions, and an untrusted-checkout carve-out (#1882, #2069) to stay safe. None of that is worth keeping for a path nobody triggers.

Proposed change

• Delete .github/workflows/claude.yml.

Explicitly out of scope

• Keep .mcp.json. The workflow passes it via --mcp-config, but it is also the project-level MCP server config the Claude Code CLI reads when working in this repo locally. It is not workflow-owned.
• Keep the github-actions Dependabot entry. main.yml still pins actions by SHA and still wants the updates.
• Revoking the ANTHROPIC_API_KEY repo secret is a repo-settings action, not a code change — worth doing once this merges, but it is not part of the diff.

Verification

• .github/workflows/main.yml is untouched and remains the only workflow.
• grep -r claude-code-action returns nothing.
• No Claude Code run is queued on the PR itself.