test: run App Intents through the system with AppIntentsTesting

[henrywang]

Closes #189

What

• New BerthlyUITests/AppIntentsSystemTests.swift: two tests that drive Berthly's intents through the system, the path Shortcuts and Spotlight use.
  • Open Container: resolves the mock worker container through Berthly's entity query, runs the intent, and checks the detail pane shows "worker".
  • Start Container: starts the stopped worker, then checks the detail pane shows the Stop button.
• Guards: #if canImport(AppIntentsTesting), because the framework ships only with Xcode 27, plus @available(macOS 27, *).
• Safety: each test launches Berthly in mock mode first. The system routes intents to the running instance, so a system-launched instance never acts on a real daemon.
• project.pbxproj: sets DEVELOPMENT_TEAM on the BerthlyUITests target only.

Why the signing change (spike result)

AppIntentsTesting answers only a test runner signed by the same development team as the app. Apple's WWDC26 session "Validate your App Intents adoption with AppIntentsTesting" states this, and I verified it locally:

Runner signing	Result
Team-signed	both tests pass
Ad-hoc (the previous default)	AppIntentsServicesSecurityErrorDomain code 800, "Your app does not have permission to perform this"
Everything ad-hoc, as ci.yml builds	same error

CI behavior

• macOS 26 leg: compiles the file out (Xcode 26).
• macOS 27 leg: builds ad-hoc, so the tests catch the code 800 error and XCTSkip. The run stays green.

So like BerthlyE2ETests, these run only on a developer's Mac, with no extra arguments: a normal ⌘U or xcodebuild test on Xcode 27 / macOS 27 includes them. Running them on CI would need a development certificate in CI secrets, which is not part of this PR.

They stay in BerthlyUITests, not BerthlyE2ETests. They use mock data, and scripts/e2e.sh re-signs its runner ad-hoc, which would make them skip.

Verification

• Local, project signing (team runner): both tests pass.
• Local, CI-style ad-hoc signing: both skip, and the run succeeds.
• Full BerthlyUITests with the team-signed runner: 84 tests, 0 failures.
• swiftlint lint --strict clean.

Local gotcha

If stale copies of app.berthly.Berthly are registered with LaunchServices (old DerivedData builds, an installed release), macOS may not see the intents, and the tests fail on "exactly one container named worker". Unregister the stale copies with lsregister -u (see the PR #188 description).

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