Unify agent-first UI and add isolated Electron desktop client

[thisisjun786]

Change

Lina now uses one agent-first interface across web/PWA and a new Electron client. Shared neutral surfaces, typography, spacing and component controls replace inconsistent styling while preserving the existing conversation, settings and onboarding controllers.

• Split portable client state into lina-client and the shared renderer into lina-ui; keep the web gateway and desktop OS adapter separate.
• Add persisted agent summaries, unread/approval/working states and stable selection. Preserve each conversation's draft, attachments and reading position through agent switches and mobile list → conversation → back navigation.
• Unify file selection and clipboard attachments, including PNG deduplication, explicit send, failed-upload recovery and session ownership.
• Replace the two confusing pane icons with one sidebar collapse control and a labeled task-only 나란히 보기 / 나란히 보기 종료 action. Hide the extra-column action when available width is insufficient, and preserve keyboard focus and task state.
• Bundle the same production renderer in Electron with an isolated profile/session directory, a restricted loopback broker and a minimal preload bridge.

New dependencies (previously absent): React/React DOM 19.2.8, Base UI 1.8.0, Electron 44.2.0, and Forge CLI/ZIP maker 8.0.0-alpha.10. shadcn base-nova source compositions provide Button, Avatar, DropdownMenu, Tabs and Combobox controls; provenance and licenses are included in packages/lina-ui/SOURCES.md and THIRD_PARTY_LICENSES.txt. Existing chat controllers retain state ownership through explicit view adapters.

The latest image-engine changes from dev are integrated into the moved shared renderer. This branch makes no additional changes to image-engine internals. Implementation, reproduction steps and remaining boundaries: implementation report.

Verification

Local checks passed after integrating dev at cd74c89:

• bun test: 1,495 passed, 0 failed across 210 files.
• bun run typecheck, bun run lint, bun run ci:validate, bun run ci:build, dependency vulnerability audit and full-history secret scan passed.
• Actual Chromium: 11 whole-app scenarios passed, covering agent switching, drafts/reading position, native clipboard → upload → explicit send → reload, failed-upload recovery, responsive navigation and first-user onboarding. The task layout and model picker checks also passed without page errors.
• The existing synthetic image service exercised generation and editing; both owned image previews rendered. External provider calls: 0.
• Linux Electron ZIP creation passed. All 11 ASAR entries matched the build; renderer JS/CSS/theme matched three isolated QA servers (rendererVersion: 8b7f0710d8fa18e241fa).

QA used isolated ports and temporary databases/session/attachment paths. Its servers have been stopped. Screenshots below are the actual web UI with synthetic fixture data; they are not Electron GUI or live-provider evidence. GitHub Lina CI run 34145635167 also passed on the PR merge candidate for head 7131663: changes, lint, types, tests, build and dev-gate all succeeded. The main-only release gate was correctly skipped.

Mobile navigation and task layout

Risks and remaining work

• Electron native GUI remains unverified because this host does not support the required sandbox setup. GUI restart, native file dialogs, notifications and protocol handling need a suitable host. No sandbox bypass was used.
• macOS/Windows packaging/signing, physical mobile IME/file interactions and updater distribution require separate qualification. Forge is pinned to an alpha version; successful Linux packaging is not release certification.
• Live image-provider quality and the world engine's final integration remain separate work. Existing integration contracts are preserved.
• The renderer extraction spans many file moves. Existing conversation/settings/onboarding behavior is covered by local tests and browser regression evidence, but native platform behavior is not implied by those checks.

This PR does not merge, promote to main, publish a release or deploy a service.