Enable implicit phase-memory activation on every warden command.

Load coordination memory by default via ensure_memory_context on app bootstrap
and route/access flows; invalidate cache after episode writes. WARDEN_MEMORY=0
remains the opt-out. Document that warden memory activate is optional only.

src/warden/worker.py

@@ -602,7 +602,9 @@ def _memory_activation_for_message(message: dict) -> tuple[Optional[dict], str]:
         return None, ""
     query = str(message.get("subject", "") or message.get("body", ""))
     try:
-        activation = warden_memory.worker_activation_context(query)
+        activation = warden_memory.ensure_memory_context(need=query, implicit=True)
+        if activation is None:
+            activation = warden_memory.worker_activation_context(query)
     except RuntimeError:
         return None, ""
     from warden.memory import format_activation_summary