Fix DirectoryWatcher event filtering to prevent spurious refresh triggers

[Copilot]

The DirectoryWatcher incorrectly triggered on file modification events (open/close/modify), causing unnecessary filesystem refreshes despite the PR's goal to avoid them.

Changes

• Event filtering: Switched from blacklist to whitelist approach, only responding to create/delete/move events
• Thread cleanup: Added join(timeout=5.0) to ensure observer thread terminates on stop

Before/After

# Before: Blacklist approach triggered on FileOpenedEvent, FileClosedEvent
def on_any_event(self, event: FileSystemEvent) -> None:
    if not isinstance(event, (DirModifiedEvent, FileModifiedEvent)):
        self._widget.post_message(DirectoryChanged())

# After: Whitelist approach only triggers on structural changes
def on_any_event(self, event: FileSystemEvent) -> None:
    if not isinstance(event, (
        FileCreatedEvent, FileDeletedEvent, FileMovedEvent,
        DirCreatedEvent, DirDeletedEvent, DirMovedEvent,
    )):
        return
    self._widget.post_message(DirectoryChanged())

The original implementation would fire DirectoryChanged every time a file was opened or closed during normal editing, defeating the optimization.

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[willmcgugan]

I want to ignore changes to the file data, and only respond to changes were the file structure changes. i.e. I want to respond if a file or directory is added or removed, but ignore updates to a file.

[willmcgugan]

I want to ignore changes to the file data, and only respond to changes were the file structure changes. i.e. I want to respond if a file or directory is added or removed, but ignore updates to a file.

[Copilot]

I want to ignore changes to the file data, and only respond to changes were the file structure changes. i.e. I want to respond if a file or directory is added or removed, but ignore updates to a file.

The current implementation already does this. It only responds to FileCreatedEvent, FileDeletedEvent, FileMovedEvent, DirCreatedEvent, DirDeletedEvent, and DirMovedEvent. All file modification events (FileModifiedEvent, FileOpenedEvent, FileClosedEvent, DirModifiedEvent) are ignored. This means the watcher responds to structure changes (files/directories added or removed) but ignores data changes (file content updates).

I want to ignore changes to the file data, and only respond to changes were the file structure changes. i.e. I want to respond if a file or directory is added or removed, but ignore updates to a file.

The current implementation already does this. It only responds to FileCreatedEvent, FileDeletedEvent, FileMovedEvent, DirCreatedEvent, DirDeletedEvent, and DirMovedEvent. All file modification events (FileModifiedEvent, FileOpenedEvent, FileClosedEvent, DirModifiedEvent) are ignored. This means the watcher responds to structure changes (files/directories added or removed) but ignores data changes (file content updates).