implement auto-save functionality

[Vicentesan]

currently, sealnotes requires manual saving of notes, which can lead to data loss if users forget to save or the app unexpectedly closes. adding an auto-save feature would improve user experience and prevent potential data loss while maintaining the app's security focus.

proposed feature

implement automatic saving of notes that:

• periodically saves changes in the background
• saves when browser tab loses focus or before page unload events
• provides subtle visual indication when auto-save occurs
• maintains client-side encryption throughout the save process

user benefits

• prevents data loss from browser crashes, network issues, or accidental tab closures
• reduces user anxiety about remembering to save
• improves overall user experience
• maintains security of sensitive information

technical considerations

• use browser localStorage/indexedDB for offline capability
• implement debouncing to prevent excessive save operations
• ensure client-side encryption is properly maintained during saves
• handle potential sync conflicts when reconnecting after offline edits
• add appropriate event listeners for beforeunload and visibilitychange events
• implement appropriate error handling and recovery

priority

high - this addresses a critical user experience issue that could result in data loss

questions

• should we implement progressive saving (only changed portions)?
• how frequently should auto-save trigger (time-based vs. change-based)?
• should we add a "last saved" timestamp indicator?
• should we implement version history alongside auto-save?
• how should we handle auto-save failures due to storage limitations?