feat(plugins): add memory slot plugin

docs/plugin.md

@@ -36,6 +36,7 @@ See [Voice Call](/plugins/voice-call) for a concrete example plugin.
 ## Available plugins (official)
 
 - Microsoft Teams is plugin-only as of 2026.1.15; install `@clawdbot/msteams` if you use Teams.
+- Memory (Core) — bundled memory search plugin (enabled by default via `plugins.slots.memory`)
 - [Voice Call](/plugins/voice-call) — `@clawdbot/voice-call`
 - [Zalo Personal](/plugins/zalouser) — `@clawdbot/zalouser`
 - [Matrix](/channels/matrix) — `@clawdbot/matrix`
@@ -137,6 +138,24 @@ Fields:
 
 Config changes **require a gateway restart**.
 
+## Plugin slots (exclusive categories)
+
+Some plugin categories are **exclusive** (only one active at a time). Use
+`plugins.slots` to select which plugin owns the slot:
+
+```json5
+{
+  plugins: {
+    slots: {
+      memory: "memory-core" // or "none" to disable memory plugins
+    }
+  }
+}
+```
+
+If multiple plugins declare `kind: "memory"`, only the selected one loads. Others
+are disabled with diagnostics.
+
 ## Control UI (schema + labels)
 
 The Control UI uses `config.schema` (JSON Schema + `uiHints`) to render better forms.