feat: inline file preview card for agent-created and filesystem files

[Eiyron]

What this adds

Whenever the agent creates or edits a file via both the create-*-file skills and the filesystem-write-text-file / filesystem-edit-file tools, a collapsible inline preview card now appears in the chat. No download required to see what was created.

Preview supports

• 30+ programming languages with VSCode-style syntax highlighting (Python, Lua, PowerShell, Batch, Shell, Rust, Go, JS/TS, C#, Java, C/C++, Ruby, PHP, SQL, YAML, and more)
• • Plain text formats: .txt, .md, .csv, .json
• • PDF rendered via inline iframe
• • Images (.png, .jpg, .gif, .webp, .svg)
• • Binary formats (PPTX, DOCX, XLSX) show a graceful "preview not available" message with download button

Files changed (7 files)

• NEW: FilePreviewCard/index.jsx — collapsible preview card component
• • ChatHistory/index.jsx — routes fileDownloadCard websocket messages to FilePreviewCard
• • HistoricalOutputs/index.jsx — uses FilePreviewCard for historical messages
• • models/files.js — adds previewUrl() and fetchText() helpers
• • agentFileServer.js — adds /preview endpoint; relaxes DB ownership check so files serve immediately before chat record is saved
• • filesystem/write-text-file.js — registers preview output via socket.send() (live) and registerOutput() (historical) after writing
• • filesystem/edit-file.js — same as above after edits

Technical notes

• Race condition fix: endpoint no longer requires a DB chat record before serving — checks storage first
• • Collapse state backed by sessionStorage so it survives streaming and scroll re-renders without jitter
• • Line numbers sync scroll with code content via JS scrollTop sync
• • /preview endpoint accepts ?token= query param for iframe/img src embedding