fix(artifacts): premium split panel + docx/pdf/xlsx in files view

[OmGuptaIND]

Summary

Three related fixes so the right-side artifact/preview UI feels like Claude's split layout instead of a cramped, leaky surface.

• Artifact panel header redesigned. Collapsed the redundant tabs + head + actions rows into a single 48px header — icon + title + type pill on the left, icon-only Source/Copy/Download/Publish + Close on the right. The tab strip now only renders when 2+ artifacts are open, and SidePanel drops its duplicate generic "Artifacts" header so the panel owns its full chrome.
• Shell outputs no longer become artifacts. Removed the `shell + content > 500` branch in `extractArtifact` — commands like `pip install …` and `python3 -c "…"` were producing pinned "Code" artifact cards keyed on their command string. They now stay as expandable tool-call chips inline.
• Files view renders rich documents. `.docx`/`.doc`/`.xlsx`/`.xls`/`.pdf` were being read as UTF-8 text and dumped into a `

  `, showing the binary container as gibberish. They now route through the existing `DocxRenderer` / `XlsxRenderer` / `PdfRenderer` components, and the preview pane was rebuilt with the same premium header bar (wider column — `minmax(420px, 560px)` — full-bleed body, icon-only reload/delete/close).

Files

• `packages/desktop/src/components/artifacts/ArtifactPanel.tsx`
• `packages/desktop/src/components/SidePanel.tsx`
• `packages/desktop/src/components/files/ProjectFilesView.tsx`
• `packages/desktop/src/lib/artifacts.ts`
• `packages/desktop/src/index.css`

Test plan

• Generate a code/markdown artifact in chat — header shows single bar (icon + title + type pill | actions + X), no duplicate "Artifacts" strip above it.
• Open 2+ artifacts — tab strip appears below the header; with one artifact, it's hidden.
• Run a long shell command (`pip install …`, `python3 -c "…"`) — output renders inline as an expandable tool-call chip, not as a "Code" artifact card.
• In the Files view, click a `.docx` — renders the formatted document (mammoth → HTML) instead of UTF-8 garbage.
• Click a `.pdf` and `.xlsx` — proper renderers fill the preview pane.
• Resize the window down to 1024px / 900px — preview width adjusts; below 900px the preview hides.
• Click the X in the preview header — selection clears and the file list reclaims the space.

🤖 Generated with Claude Code