feat(server-02): promote EventStore to global-sequence store with subscribeAll

StoredEvent gains sessionSequence: Long (per-session monotonic); existing
sequence field becomes the global monotonic cursor across the entire store.
SqliteEventStore allocates both counters inside the same BEGIN IMMEDIATE
transaction and emits to a global MutableSharedFlow after commit.
InMemoryEventStore mirrors this with an AtomicLong global counter and a
suspend-on-overflow SharedFlow. EventStore interface gains subscribeAll()
and lastGlobalSequence(). Contract tests updated and extended to cover
global-sequence and cross-session subscribeAll invariants.

apps/server/src/main/kotlin/com/correx/apps/server/logging/LoggingEventStore.kt

@@ -61,4 +61,8 @@ class LoggingEventStore(private val delegate: EventStore) : EventStore {
 
     override fun allEvents(): Sequence<StoredEvent> = delegate.allEvents()
     override fun allSessionIds(): Set<SessionId> = delegate.allSessionIds().also { log.debug("got session ids from store: {}", it) }
+
+    override fun subscribeAll(): Flow<StoredEvent> = delegate.subscribeAll()
+
+    override suspend fun lastGlobalSequence(): Long = delegate.lastGlobalSequence()
 }