fix: recover chat source replies

[rogerchappel]

Summary

• treat tool-backed Done. / completion-status chat finals as placeholders instead of visible answers
• recover the visible message from OpenClaw chat history, matching Dashboard's projected message-tool reply path
• read nested sourceReply payloads from tool result/details/metadata shapes

Verification

• pnpm vitest run src/app/api/chat/route.test.ts
• pnpm typecheck
• pnpm lint (passes with existing warnings)
• git diff --check
• pre-push hook: pnpm typecheck && pnpm build (build passes with existing Turbopack NFT warnings)

Risk

Medium: changes normal chat final-answer selection for tool-backed placeholder replies; no auth, data, config, or migration changes.