fix(web): copy terminal selection instead of a blank clipboard - #7678

💭 This diff is about terminal surface code, not Effect services — the changed files are the ghostty surface implementation and its tests, with no Effect service creation involved. I'll do a quick sanity check to confirm there's no Effect usage in these files before concluding it's all clear. There's no Effect service code here, so everything's clear. Since the response still needs to follow the JSON schema, I'll set the summary field to "All clear" to satisfy both the instruction and the format requirement.