refactor: strip v0.39 surfaces — Workbench, Skills, Marketplace, Lab, MaaS

Phase 1.4 + 1.5: wipe everything not directly part of AI conversation
search. Replace with minimal skeletons that compile.

Backend (src-tauri):
- Delete all src-tauri/src/app/* modules except for a fresh, empty
  lib.rs that boots Tauri with five plugins (opener, dialog, process,
  updater, global-shortcut) and registers a single `ping` command.
- Delete claude_web_sync, hook_watcher, pty_manager, diagnostics.
- Slim Cargo.toml deps to: lovcode-core + tauri stack + shared
  workspace deps. Drop portable-pty, arboard, rusqlite, aes/cbc,
  cocoa/objc, security-framework, zip, reqwest, jieba (moved to core),
  tantivy (moved to core), notify (moved to core), and ~15 others.
- tauri.conf.json: drop third-parties bundle resources.

Frontend (src/):
- Wipe every page, view, component, store, hook, lib, type module from
  the v0.39 era. Replace with: main.tsx + router on top of
  vite-plugin-pages, pages/index.tsx (search stub with a `ping`
  button), pages/search-overlay.tsx (floating window placeholder),
  index.css with the warm-academic palette.
- Slim package.json: drop monaco, xterm, recharts, jotai, framer-motion,
  react-query, all radix primitives, lodash, date-fns, lovinsp, and
  every other dependency that only existed for the deleted surfaces.
- Rewrite index.html and vite.config.ts to match.

Top-level cleanup:
- Remove third-parties/ submodules (claude-code-docs, codex,
  claude-code-templates, claude-plugins-official) — they were only used
  by the docs/marketplace pages.
- Remove marketplace/, scripts/agent-chat-harness.mjs, update-icon.sh,
  components.json, design-guide.md, and the v0.39 spec/research markdown
  files at repo root.

Build status:
- `cargo build --workspace` ✔
- `pnpm build` ✔

The legacy code is preserved on the `legacy/v0.39-workbench` branch
already pushed to origin.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: MarkShawn2020