Remove Migrate Agents sidebar shortcut

Keep the migration UI available from the Plugins screen and update its documentation and ownership notes.

plugins/_migrate_agents/AGENTS.md

@@ -8,7 +8,7 @@
 
 - `helpers/migration.py` owns source parsing, redaction, limits, preview data, and native chat conversion.
 - `api/migration_preview.py` owns read-only upload inspection; `api/migration_import.py` owns confirmed writes.
-- `webui/` and the sidebar extension own source selection, upload, review, consent, and progress UI.
+- `webui/` owns source selection, upload, review, consent, and progress UI.
 - `tests/` owns parser, privacy, archive-safety, native-chat, project, and import-helper regression coverage.
 
 ## Local Contracts

plugins/_migrate_agents/README.md

@@ -17,7 +17,7 @@ Credentials, authentication files, and hidden reasoning are excluded.
 
 ## Enable
 
-Enable **Migrate Agents** in Plugins, then use the inbox button beside Dashboard.
+Enable **Migrate Agents** in Plugins, then use its **Open** button.
 
 ## Prepare an export
 

plugins/_migrate_agents/extensions/webui/sidebar-quick-actions-main-start/migrate-agents.html

@@ -1,10 +0,0 @@
-<div x-data>
-  <button x-move-after=".config-button#dashboard"
-          class="config-button"
-          id="migrate-agents"
-          title="Migrate Agents"
-          aria-label="Open Migrate Agents"
-          @click="openModal('/plugins/_migrate_agents/webui/main.html')">
-    <x-icon name="move_to_inbox"></x-icon>
-  </button>
-</div>