Fix universal upload progress

[OmGuptaIND]

Summary

• allow composer and Files uploads to use the same chunked upload flow for any file type
• add upload progress tracking in the desktop Activity dock so users can see active/recent uploads and byte progress
• support video/generic file artifacts, including .mov MIME classification and video preview rendering

Root Cause

• composer uploads were split between inline model attachments and project file uploads, with file input constraints and drag/drop behavior that effectively excluded files like .mov
• filesystem writes sent whole files as base64 JSON payloads with no progress protocol, so large files had no visible side UI or reliable upload feedback
• artifact classification did not include video or generic fallback render types, so non-document uploads degraded poorly after upload

Validation

• pnpm exec biome check --write packages/agent-server/src/server.ts packages/desktop/src/components/ActivityDock.tsx packages/desktop/src/components/artifacts/ArtifactPanel.tsx packages/desktop/src/components/artifacts/ArtifactRail.tsx packages/desktop/src/components/artifacts/VideoRenderer.tsx packages/desktop/src/components/chat/ArtifactCard.tsx packages/desktop/src/components/chat/ChatInput.tsx packages/desktop/src/components/chat/MessageBubble.tsx packages/desktop/src/components/chat/SessionFilesBar.tsx packages/desktop/src/components/files/ProjectFilesView.tsx packages/desktop/src/lib/artifacts.ts packages/desktop/src/lib/connection.ts packages/desktop/src/lib/fileUploads.ts packages/desktop/src/lib/store/index.ts packages/desktop/src/lib/store/uploadStore.ts packages/desktop/src/lib/uploadDefaults.ts packages/desktop/src/lib/workspaceArtifacts.ts
• pnpm --filter @anton/desktop typecheck
• pnpm --filter @anton/agent-server build
• git diff --check