* feat: add 'Open files in preview mode' setting
- Add defaultFileViewerPreview setting to persist user preference for file viewer default mode
- Add checkbox in Settings → Sessions → Session Defaults to toggle the setting
- Files now open in preview mode by default when setting is enabled
- Respects per-file-type localStorage persistence for markdown/HTML/JSON files
- Setting persists across sessions via /api/config/settings endpoint
* fix: address PR review feedback
- FilesView: respect HTML localStorage preference in file-change effect,
falling back to global setting only when nothing stored
- DefaultsSettings: read defaultFileViewerPreview directly from config store
instead of redundant local state + separate fetch
- DefaultsSettings: extract duplicated toggle logic into
handleToggleFileViewerPreview callback
* fix: honor default preview setting for markdown files
Previously mdViewMode only read localStorage on mount (deps: []), so
when settingsDefaultFileViewerPreview was enabled and no MD_VIEWER_MODE_KEY
was stored, markdown files silently opened in edit mode — ignoring the
setting for the very file type users most want to preview.
Fold md init into the per-file-change effect, mirroring the html handling:
localStorage preference wins, falling back to the setting-derived default.
The saveMdViewMode callback stays untouched so user-initiated toggles
still persist.
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Co-authored-by: Bohdan Triapitsyn <artmore@protonmail.com>
