feat(flow-chat): render view_image previews inline

[wgqqqqq]

Summary

• carry optional tool image attachments through completed tool events and persisted session history
• render successful view_image results as a compact, auto-expanded image attachment in Flow Chat
• open the thumbnail in the existing large image modal and keep unsupported MIME types out of the DOM
• use the backend-produced attachment instead of reading toolCall.input.path in the UI, so local, web, peer-device, and remote workspace flows share the same rendering path

Closes #1490

Prior contribution

This work builds on the product need reported by @liuxingyu521 in #1490 and the dedicated Flow Chat image-preview direction first implemented and demonstrated by @liuxingyu521 in #1491. That PR established the value of showing view_image output directly in the conversation and provided the first card/preview implementation.

This PR carries that contribution forward on the latest main after #1491 was closed for being stale. It preserves the dedicated-card UX while addressing the remote-workspace concern raised in that discussion: image bytes now come from the tool's existing ToolImageAttachment, flow through the stable completed-event contract, and survive session history restoration instead of requiring the frontend to reopen a local path.

Type and Areas

Type: Feature / UI/UX

Areas: Rust core, event contracts, session persistence, Web UI

Verification

• pnpm run type-check:web
• pnpm --dir src/web-ui run test:run src/flow_chat/tool-cards/ViewImageToolCard.test.tsx src/flow_chat/services/flow-chat-manager/ToolEventModule.test.ts (13 tests passed)
• pnpm run i18n:audit
• cargo test -p bitfun-events -p tool-runtime completed (6 focused tests passed)
• cargo test -p bitfun-core view_image_reads_remote_workspace_relative_image
• cargo check -p bitfun-core -p bitfun-events -p tool-runtime -p bitfun-services-core -p bitfun-acp

Reviewer Notes

• image_attachments is optional on the event and persistence DTOs, preserving compatibility with existing tool results and saved sessions.
• The preview accepts only PNG, JPEG, GIF, WebP, and BMP attachments. The backend already optimizes the image to provider limits before attaching it.
• The compact row and 160px thumbnail follow the image-attachment presentation suggested in the feat(web-ui): 为 view_image 工具增加对话内图片预览卡片 #1491 discussion; clicking the thumbnail opens the existing modal.
• AI-assisted implementation; verification level: focused automated checks plus remote-workspace regression coverage.