feat(workspace): per-session workspace-scoped tools, policy, and undo

Compute the effective tool registry/executor and plane-2 WorkspacePolicy per run
from config.workspace (effectivesFor), threaded through the orchestrators; a null
workspace falls back to the boot instances byte-for-byte. Wire the concrete
WorkspaceToolRegistryProvider in Main (buildToolConfigForWorkspace). Session undo
unions the session's recorded workspace into its jail roots. (Axis 2 Phase A, tasks 3 + 7.)

testing/integration/build.gradle

@@ -25,4 +25,6 @@ dependencies {
     testImplementation(project(":testing:contracts"))
     testImplementation(testFixtures(project(":testing:contracts")))
     testImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-test:1.9.0")
+    testImplementation(project(":infrastructure:tools"))
+    testImplementation(project(":infrastructure:tools:filesystem"))
 }