feat: group consecutive tool calls with verb labels and improved UI

[tellaho]

Summary

• Consecutive same-type tool calls collapse into expandable groups ("Edited 3 files", "Ran 2 commands") with animated slide-in transition
• Solo tool calls show past-tense verb + filename labels ("Edited content-design-review.md") with layout-animated trigger that hides filename on expand
• Per-tool artifact candidates instead of single primary host per message — each tool call shows its own open-file action
• Artifact actions render as inline filename + arrow-up-right link below code block, clickable to open file
• Groups split by execution outcome so errors aren't hidden behind success labels
• Redundant bottom labels (e.g. bare "Ran") hidden when they add no info beyond the trigger
• Extracted ToolChainCards and toolLabelUtils into dedicated files

Screen.Recording.2026-04-03.at.9.55.35.AM-compressed.mp4

Test plan

• Verify consecutive same-type tool calls collapse into expandable group row
• Verify solo tool calls show "Edited filename.md" with chevron, filename disappears on expand
• Verify expanding solo tool call shows content with left border + filename link below
• Verify clicking filename link opens the file
• Verify grouped items show just filename with arrow-up-right link
• Verify failed tool calls are not grouped with successful ones
• Verify labels like "Ran" or "Delegate" don't show redundantly below expanded content

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