test: add ShotdeckTests target — real launch/bootstrap wiring regression (coverage gap)

The Core-level regression tests added for the launch-paths BLOCKER
(ReturnWatcherTests.swift) hand-replicate what AppDelegate.makeLaunchModel()
and AppModel.bootstrap() do, rather than calling them — a future revert of
either would not fail `swift test`. Neither lives in ShotdeckCore, so
ShotdeckCoreTests cannot reach them; this new test target depends on the
Shotdeck executable target itself and uses @testable import (confirmed this
works cleanly with SwiftPM despite Shotdeck's main.swift top-level-code entry
point — no separate main-symbol conflict).

realLaunchModelAndBootstrapDetectAMarkedOneDriveReturn persists
transport=.oneDrive (UserDefaults.standard, snapshot-and-restore — the same
established pattern PickerSelfTest's ONEDRIVE-SELFTEST phase already uses,
since neither of these real call sites has any defaults-threading to plug an
isolated suite into), calls AppDelegate.makeLaunchModel(appSupportRoot: <temp>)
and awaits model.bootstrap() UNMODIFIED, then drops a marked-up Redline PDF
into the temp OneDrive folder and asserts the watcher reports it.

Verified this test actually catches the original blocker: temporarily
reverted makeLaunchModel() to the AirDrop-only resolver, and separately
reverted bootstrap()'s updateWatchFolder reconcile — both reproduce the
failure (the discarded revert is not part of this commit).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012ZiTXPbPCSjzPVsfoweAbp

Package.swift

@@ -27,5 +27,14 @@ let package = Package(
             dependencies: ["ShotdeckCore"],
             swiftSettings: [.swiftLanguageMode(.v6)]
         ),
+        // Exercises the real Shotdeck-app-target wiring (AppDelegate.makeLaunchModel(),
+        // AppModel.bootstrap()) via @testable import — logic ShotdeckCoreTests cannot
+        // reach because it only depends on ShotdeckCore, not the Shotdeck executable
+        // target itself. See ReturnWatcherLaunchWiringTests.swift.
+        .testTarget(
+            name: "ShotdeckTests",
+            dependencies: ["Shotdeck", "ShotdeckCore"],
+            swiftSettings: [.swiftLanguageMode(.v6)]
+        ),
     ]
 )