CI: rename everything-mcp-diff.yml to mcp-interface-diff.yml, staged across a milestone merge [Step 2] #5527

Problem

Step 2 of the staged rename in #5463. Step 1 adds mcp-interface-diff.yml beside everything-mcp-diff.yml (workflow_dispatch-only, callers unchanged) so that it reaches main in a milestone merge. GitHub dispatches a workflow only when its file exists on the default branch, so the callers can switch to the new name only once that merge has landed.

Expected behavior

Once #5463 is on main (the v2.5.0 milestone merge):

1. Point both dispatch loops (version-packages.yml, prepare-python-release.yml) and their gh run list --workflow calls at mcp-interface-diff.yml.
2. Update TOOLING_PATHS in scripts/lib/interface-diff-servers.mjs and scripts/version-pr-ci.test.mjs.
3. Update RELEASING.md, the release skill, docs/quality-gate.md and the AGENTS.md tree.
4. Give mcp-interface-diff.yml the full push / pull_request triggers and delete everything-mcp-diff.yml.

The first version PR after this lands still gets its Interface diff (dispatched) status.

Notes

Blocked on #5463 shipping to main. Do not start before that milestone merge.

Related: #5428, #5459, #5463.