fix: clarify edit/write success in diagnostics output

[Lyapsus]

Summary

• clarify that edit/write succeeded even when LSP diagnostics are reported, so agents do not misread errors as failed changes
• keep output minimal to align with the "no problems - no output" philosophy by only adding the line when diagnostics exist
• a universal success line for all tools could be a cleaner long-term approach but would likely be noisier

Fixes #9102

Testing

• manual: local tool invocation via bun -e

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