feat: scaffold cross-session router memory (L3) with turbovec sidecar

Defines the L3MemoryStore contract in core:router (entry, query, hit,
in-memory test default) and a new infrastructure:router:turbovec module
that adapts turbovec via a Python sidecar over stdin/stdout JSON-Lines.

Adapter manages the subprocess via ProcessBuilder with lazy start,
mutex-serialized requests, and shutdown via withTimeout. Wire-format
metadata that turbovec doesn't store (sessionId, turnId, text) is kept
in an in-memory map for now — durable persistence ships with the
upcoming ChatTurnEvent.

Not yet wired into RouterFacade, InfrastructureModule, or DI. Embedding
generation source is a separate concern.

infrastructure/router/build.gradle

@@ -0,0 +1,12 @@
+plugins {
+    id 'java-library'
+    id 'org.jetbrains.kotlin.jvm'
+    id 'org.jetbrains.kotlin.plugin.serialization'
+}
+
+dependencies {
+    implementation project(':core:router')
+    implementation project(':core:events')
+    testImplementation "org.junit.jupiter:junit-jupiter"
+    testImplementation "org.jetbrains.kotlinx:kotlinx-coroutines-test"
+}