revert(panel): restore w as multi-file selection toggle

[dlyongemallo]

Closes #124.

See #66 for context.

[Copilot]

Pull request overview

Restores the default multi-file selection toggle in Diffview’s file panel back to w, aligning the runtime defaults with the documented defaults and removing guidance that was only necessary when the toggle was bound to <Space> (leader-key conflict).

Changes:

• Change the default file_panel keymap for actions.toggle_select_entry from <Space> back to w.
• Update user docs to reflect w as the toggle key.
• Remove the <Space>/leader-key conflict tip since it no longer applies to the defaults.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
lua/diffview/config.lua	Restores w as the default file-panel multi-select toggle key.
doc/diffview_defaults.txt	Updates default-config documentation to match the restored w mapping.
doc/diffview.txt	Updates keymap reference section and removes now-irrelevant <Space> remap example.
TIPS.md	Removes the <Space> leader-key conflict workaround tip (no longer relevant to defaults).

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