Find the packaged zmx beside the Windows daemon

[coneilen]

Summary

The packaged Windows daemon could not find zmx. The package installs zmx.exe
beside graphcoded.exe under %LOCALAPPDATA%\GraphCode\current\bin, and nothing
copies it into the support directory. ZmxLocator looked only at
%USERPROFILE%\.graphcode\bin\zmx.exe, so isInstalled was false.

As a result, the daemon silently skipped every zmx operation:

• loop launches failed with "zmx is not installed";
• stop requests could not be delivered;
• kills and the condemned-session reaper did nothing;
• Stop wrote "its session could not be reached, so it was killed" to the memory
  log while the session kept running.

That is the beta9 Dev Box section 6A TerminalSessionOwnership failure, and it
matches beta8's "Stop left the Copilot process alive".

Changes

• GraphcodeKit/Sources/Sessions/ZmxLocator.swift: on Windows, resolve zmx.exe in
  the running executable's directory first, then fall back to the support bin. When
  neither exists, the support path is still reported, so isInstalled stays false.
  The pure helpers candidates(...) and resolve(...) compile on every platform.
  macOS keeps ~/.graphcode/bin/zmx exactly.
• windows-tests/WindowsDaemonTests.swift: Windows XCTest for sibling-first order,
  the support-bin fallback, the neither-present case, and a missing executable
  directory.
• graphcode/Tests/SupportDirectoryTests.swift: a macOS Swift Testing check of the
  same resolver, which also asserts that macOS binaryURL is still the support bin.

Test plan

Windows, pinned Swift 6.3.3 (process-local SDKROOT/PATH as in
Tools/windows/validate.ps1):

RED: swift-test --package-path . --filter WindowsDaemonTests.testZmxLocator -> 1 of 3 failed, candidates returned only C:/Users/u/.graphcode/bin/zmx.exe and the packaged sibling was not preferred
GREEN: swift-test --package-path . --filter WindowsDaemonTests.testZmxLocator -> 3/3 passed
REGRESSION: swift-test --package-path . on Windows -> 103 XCTest and 6 Swift Testing tests passed, 0 failures

Also run:

• swift-format lint --strict --configuration .swift-format on the three changed
  files -> exit 0.
• swift-build --configuration release --product graphcoded and --product graphcode -> both built.
• End-to-end in the packaged layout: graphcoded.exe, graphcode.exe and
  zmx.exe side by side, an isolated support directory with no bin\zmx.exe, a
  main loop with a live graphcode-UUID session, then graphcode node stop:
  • beta9 daemon (sha256 2eb05ba3…): memory log "could not be reached, so it
    was killed", but the session survived with the same PID. Fails the Dev Box
    Stop contract (Correct the Dev Box Stop qualification contract #637).
  • this branch's daemon (sha256 4a68a2a2…): memory log "asked to stop
    looping", the session kept its PID, and zmx history showed
    [graphcode] Stop requested from the graph in that session only. Passes the
    Stop contract.
• macOS: the maintainer ran the branch on a Mac and reported the macOS tests
  passed. Exact counts were not supplied here.

Not run: the Windows shell/UIA live gates and packaging validation (no shell
code changed), and a fresh packaged Dev Box run. That requalification needs a new
candidate.

Checklist

• I have read the Contributing Guidelines
• I have signed off my commits (git commit -s) per the DCO
• Tests pass locally (make test) — reported passing on macOS by the maintainer
• Code follows the existing style (make check) — swift-format strict passed on Windows; SwiftLint result not separately reported
• I added the test/contract before the implementation and observed the intended RED failure