Add a 'Copy All' button to copy every output at once

[zanni098]

Context

Each generated output (markdown, config, checklist) has its own copy button in src/components/Generator.tsx, but there is no way to copy all three at once. Users who want all outputs have to click copy three times, or use "Download All" and then open the files.

Task

Add a "Copy All" action.

• Add a button near the "Download All" button (right side of the preview column) that copies the three outputs as a single well-formatted text bundle (e.g. separated by --- and a filename header per block).
• Reuse the existing copied/check feedback pattern — show a checkmark briefly on success.
• Follow the existing visual style of the action buttons.

Acceptance criteria

• A "Copy All" button exists in the preview area
• Clicking it puts all three outputs (markdown, config, checklist) into the clipboard, each labeled with its filename
• Feedback state (check icon) matches the existing copy buttons
• npm run build passes

Related

• src/components/Generator.tsx — CodeBlock copy handling (~line 31) and the action row (~line 192)