fix: improve offline editor save safety - #80

Summary

This PR makes a focused stability pass on NexaNote before more UI work:

• Flushes pending typed text before switching between Text and Draw mode, so text typed in the debounce window is not skipped when the canvas opens.
• Saves page text regardless of whether the Draw canvas is currently visible, preventing Text → Draw mode switches from dropping recent text edits.
• Adds a lightweight Note.copyWith helper for the API DTO so the editor can update its local title snapshot after a successful save.
• Aligns metadata/com.nexanote.app.yml with the current app/pubspec.yaml version 1.1.4+9.
• Updates the Android release workflow comment so it matches the current Prepare Release → release PR → tag-from-main flow.

Manual test checklist

• Install app / open existing NexaNote build.
• Use offline mode.
• Create a note.
• Type text, then immediately tap Draw before autosave delay finishes.
• Draw strokes.
• Leave/reopen the note.
• Confirm typed text still exists.
• Confirm drawing still exists.
• Confirm Settings → About still shows the installed version.
• Confirm Obtainium/GitHub release flow still uses NexaNote-Android.apk.

Notes

This is intentionally not a giant redesign PR. The next PR should do deeper Settings UI polish and canvas gesture work, especially two-finger pan/zoom vs drawing behavior.