* add version pinning

* fix: split workload update and restore to allow rollback file

dotnet workload restore --from-rollback-file fails because the command
internally invokes install with --skip-manifest-update, which conflicts
with --from-rollback-file. Use update first to pin manifest versions,
then plain restore to install workloads using those pins.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* fix: pin iOS/maccatalyst TargetPlatformVersion to 18.2

The workload manifest pin alone wasn't enough — the macos-26 runner has
the iOS 26.2 SDK pack pre-installed, so MSBuild resolved net9.0-ios to
the highest available TPV (26.2.9008), which requires Xcode 26.3.

Pinning the TPV explicitly (net9.0-ios18.2, net9.0-maccatalyst18.2)
forces MSBuild to use the 18.2 SDK pack regardless of what newer packs
are installed on the runner.

Updates the workflow build/output paths, UITests path lookup, and README
examples to match.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Update dotnet-maui/global.json

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* revert workload pin, use latest .NET iOS workload with Xcode 26.3

The workload manifest pin (18.2.9173) didn't expose a usable TPV path
on the macos-26 runner — NETSDK1140 listed only 18.0 and 26.2 as valid.
Rather than fight pack resolution, take the simpler route: use the
latest workload and pin Xcode to 26.3 (which is what 26.2.9008 needs).

Keeps the SDK pin in dotnet-maui/global.json and the explicit Xcode
selection in CI so the "out of sync Xcode/.NET iOS" failure mode is
still controlled, just from the Xcode side.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>