Route loaded module logging under the mvt.ext namespace

Modules loaded from installed packages or file paths live outside the
mvt logger hierarchy, so their log records never reach MVT's console
and file handlers and instead fall through to logging.lastResort:
alerts print as bare unformatted lines and INFO messages are dropped
entirely.

Add get_module_logger() and use it everywhere module loggers are
created. Built-in mvt.* modules keep their existing logger names, and
everything external is parented under a dedicated mvt.ext namespace so
records reach the handlers and external names can never collide with
MVT's internal logger tree. File-path modules are named after their
file (mvt.ext.<stem>) instead of the mangled internal import name.

Document a naming convention for community module packages:
distribute as mvt-plugin-<name> with import package mvt_plugin_<name>,
including the publishing organization in the name. The prefix is
advisory (loading is by entry point, and it is no mark of
authenticity), but conforming packages get a cleaner logger namespace:
the mvt_plugin_ prefix is stripped, so mvt_plugin_amnesty_custom logs
as mvt.ext.amnesty_custom.

tests/common/test_module_loader.py

@@ -3,10 +3,12 @@ import pytest
 from mvt.common.module import MVTModule
 from mvt.common.module_loader import (
     CustomModuleLoadError,
+    get_module_logger,
     load_custom_modules,
     load_custom_modules_from_path,
     module_supports_command,
 )
+from mvt.ios.modules.mixed.whatsapp import Whatsapp
 
 
 MODULE_TEMPLATE = """
@@ -144,3 +146,44 @@ def test_module_supports_command_honors_supported_commands(tmp_path):
 
     assert module_supports_command(module, "ios", "check-backup")
     assert not module_supports_command(module, "ios", "check-fs")
+
+
+def test_get_module_logger_keeps_builtin_names():
+    assert get_module_logger(Whatsapp).name == "mvt.ios.modules.mixed.whatsapp"
+
+
+def test_get_module_logger_parents_package_modules_under_mvt_ext():
+    class PackageModule(MVTModule):
+        pass
+
+    PackageModule.__module__ = "some_plugin_package.ios.custom"
+
+    assert (
+        get_module_logger(PackageModule).name
+        == "mvt.ext.some_plugin_package.ios.custom"
+    )
+
+
+def test_get_module_logger_strips_the_plugin_package_prefix():
+    class PluginModule(MVTModule):
+        pass
+
+    PluginModule.__module__ = "mvt_plugin_amnesty_custom.ios.custom"
+
+    assert get_module_logger(PluginModule).name == "mvt.ext.amnesty_custom.ios.custom"
+
+
+def test_get_module_logger_only_strips_the_prefix_from_the_top_level():
+    class NestedModule(MVTModule):
+        pass
+
+    NestedModule.__module__ = "other_package.mvt_plugin_sub"
+
+    assert get_module_logger(NestedModule).name == "mvt.ext.other_package.mvt_plugin_sub"
+
+
+def test_get_module_logger_names_path_modules_after_their_file(tmp_path):
+    module_path = _write_module(tmp_path / "my_custom_module.py", "PathModule")
+    module = load_custom_modules_from_path(str(module_path))[0]
+
+    assert get_module_logger(module).name == "mvt.ext.my_custom_module"