fix: show edit warning dialog only once per session

[roomote]

This PR fixes issue #6058 where the edit warning dialog was shown every time a message was edited, creating a frustrating user experience.

Changes

• Added hasShownEditWarning flag to ClineProvider class to track if the warning has been shown in the current session
• Modified handleEditOperation in webviewMessageHandler.ts to check this flag before showing the dialog
• If the flag is false (first edit), show the dialog and set the flag to true
• If the flag is true (subsequent edits), skip the dialog and proceed directly with the edit
• Updated tests to reflect the new behavior

Testing

• All existing tests pass
• Added new test case to verify that subsequent edits do not show the dialog
• Updated existing test to verify that the first edit shows the dialog

Fixes #6058

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Important

Fixes issue #6058 by showing the edit warning dialog only once per session using a session-based flag in ClineProvider.

• Behavior:
  • Adds hasShownEditWarning flag to ClineProvider to track if edit warning dialog has been shown in the current session.
  • Modifies handleEditOperation in webviewMessageHandler.ts to check hasShownEditWarning before showing the dialog.
  • Shows dialog on first edit and sets flag to true; skips dialog on subsequent edits.
• Testing:
  • Updates existing tests to verify dialog shows on first edit and not on subsequent edits.
  • Adds new test case for subsequent edits without dialog.
• Misc:
  • Fixes issue Edit warning dialog appears on every edit #6058.

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