Fix multiline edit loss when saving from editor (#75)

[jonaraphael]

Summary

• Resolve [BUG] In a multi-line CSV file, a row disappear when a line break occurs. #75: prevent multiline cell edits from being lost when saving via Ctrl/Cmd+S while a cell is still in edit mode
• Scope decision: in-scope (friendly)

Changes

• Delay webview save message until after blur commits the current edit message
• Add regression coverage in webview shortcut tests for Ctrl/Cmd+S ordering

Validation

• npm run compile
• npm test

Risk Notes

• Touches only edit-mode save keyboard handling in webview script
• Save now runs on next macrotask after blur; this is intentional to preserve commit ordering

Human Review Request

• Requested reviewer: @jonaraphael
• Please review behavior in: multiline editing + save flow
• Specific decision needed: confirm this resolves the reported repro steps on your environment

Fixes #75