Remove debug console.log statements from session restore

[Copilot]

Addresses review feedback to remove debug logging from session restore functionality before production merge.

Changes:

• Removed 5 console.log('[SESSION] ...') debug statements from file open and session save flows
• Replaced console.error with log.error using existing electron-log utility
• Removed empty .then() callback that only contained debug logging

Example:

// Before
console.log('[SESSION] Saving session with files:', allOpenedFiles)
dataCenter.setItem('lastSession', allOpenedFiles).then(() => {
  console.log('[SESSION] Session saved successfully')
}).catch(err => {
  console.error('[SESSION] Failed to save:', err)
})

// After
dataCenter.setItem('lastSession', allOpenedFiles).catch(err => {
  log.error('[SESSION] Failed to save:', err)
})

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