fix(dispatch): polish user-facing setup UX

[bobleer]

Summary

• replace capability identifiers, protocol diagnostics, and raw backend errors with concise user-facing states and recovery actions
• improve target readiness, source-build, model-sync, permission, navigation, and result-retrieval interactions
• move necessary technical details behind progressive disclosure and update English, Simplified Chinese, and Traditional Chinese copy
• add regressions that prevent internal capability names and transport diagnostics from leaking into the UI

Testing

• pnpm --dir src/web-ui run test:run src/features/dispatch src/flow_chat/components/ChatInputWorkspaceStrip.test.tsx src/flow_chat/components/ChatInputWorkspaceStripLayout.test.ts src/app/components/NavPanel/sections/sessions (131 tests passed)
• pnpm run type-check:web
• pnpm run i18n:audit
• pnpm run theme:color-audit:all
• pnpm run lint:web (0 errors; 2 existing warnings)