fix(plugins): read memory plugin.yaml as UTF-8

[Tianworld]

Memory provider discovery reads each provider's \plugin.yaml\ for descriptions (two call sites). Both used the process default text encoding; on Windows, valid UTF-8 YAML with non-ASCII text could fail inside broad \except\ handlers and hide descriptions.

[alt-glitch]

Likely duplicate of #8450 — same UTF-8 fix for plugin.yaml in memory setup. Also related to #15519 (broader encoding fix) and #9891 (plugin manifest locale decoding).

[teknium1]

Thanks for the focused Windows compatibility fix. This automated hermes-sweeper review found that the exact behavior is already implemented on current main.

• plugins/memory/__init__.py:161 reads provider plugin.yaml files with encoding="utf-8-sig" in discover_memory_providers().
• plugins/memory/__init__.py:427 applies the same UTF-8-compatible decoding in discover_plugin_cli_commands().
• Commit d682f320b35a13084371a541a835e1d988c982b8 introduced the current file containing both guarded reads. utf-8-sig also accepts ordinary UTF-8 while handling a UTF-8 BOM.
• This matches the duplicate relationship with fix(memory): read plugin.yaml as UTF-8 in memory setup #8450 noted in the existing discussion.

Closing as implemented on main.