Remove the retired merge-queue and devbox folders (#364)

[obj-p]

Part of #364: the local VM merge queue is retired in favor of CI on the self-hosted mini runner (#361).

Removes merge-queue/ and devbox/ from main via git rm -r. This includes the stale bar.swift (still had --flaky_test_attempts=3 and the removed remote cache), which becomes moot with the deletion.

vzy/ is intentionally kept: it was extracted to https://github.com/obj-p/vzy (#363), and #364 defers its removal from this repo until the new repository is verified.

Verified nothing in the Bazel graph, scripts, or workflows references the deleted folders (the only merge-queue/devbox grep hits outside the deleted trees are historical prose comments in two BUILD.bazel files). bazel run //tools/lint:check passes.

🤖 Generated with Claude Code

https://claude.ai/code/session_01GD1gCDkmhug8VunhqpF7rN

[obj-p]

CI red, but classified as the known pre-existing flake, not this change: MCPIntegrationTests failed 1 of 21 tests with APPSERVER-ATTR site=mjpeg-body exit=threw ... NSURLErrorDomain code=-999 ... thrown: code=-1 on stream.mjpeg — the appServerEndToEnd NSURLError-1 issue tracked in #320 (instrumentation ongoing on 350-appserver-attribution). All other 10 test targets passed, including CLIIntegrationTests and IOSPreviewE2ETests. This PR only deletes merge-queue/ and devbox/, which nothing in the Bazel graph references. Not retrying and not merging per the decommission ground rules; leaving the merge decision to the owner.