chore(email): sharpen tool descriptions and rename email_list_inbox

- Rename email_list_inbox → email_list_folder (works on any folder, not just inbox)
- email_list_folder / email_search: distinguish browse-by-recency vs filter-by-query
- email_move / email_delete: clarify single-email scope; point to email_bulk_action for multiple
- email_bulk_action: clarify it handles multiple emails; point to move/delete for single
- email_create_folder: remove redundant "ask user" instruction (requires_approval handles it)
- Update tests to reflect renamed tool

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/unit/test_email_plugin.py

@@ -351,7 +351,7 @@ def test_plugin_exposes_16_tools():
     assert len(tools) == 16
 
     expected = {
-        "email_list_inbox", "email_read", "email_send", "email_reply",
+        "email_list_folder", "email_read", "email_send", "email_reply",
         "email_forward", "email_move", "email_delete", "email_mark_read",
         "email_search", "email_list_folders", "email_create_folder",
         "email_inbox_summary", "email_list_rules", "email_create_rule",
@@ -378,7 +378,7 @@ def test_read_tools_no_approval():
     plugin.on_load(lambda _: None)
     tools = {t.name: t for t in plugin.tools()}
 
-    for name in ["email_list_inbox", "email_read", "email_mark_read",
+    for name in ["email_list_folder", "email_read", "email_mark_read",
                  "email_search", "email_list_folders", "email_inbox_summary",
                  "email_list_rules"]:
         assert not tools[name].requires_approval, f"{name} should NOT require approval"