refactor: archive GUI clients; keep minimal TUI with hooks/API

Move Qt/Tauri/full Web SPA under archive/, ship hermit as CLI/TUI plus
libcstcore and cst-webui/1 HTTP+SSE (turn lifecycle hooks, capabilities).

Co-authored-by: Cursor <cursoragent@cursor.com>

archive/README.md

@@ -0,0 +1,22 @@
+# archive/ — frozen clients (not shipped with Hermit)
+
+This tree holds **reference front ends** that used to live in the main repo.
+The Hermit product surface is now:
+
+- **CLI + minimal TUI** (`hermit`)
+- **Engine library** (`libcstcore.a` + `include/`)
+- **Replaceable extensions**: plugins / MCP / skills / agents (not core tools)
+- **Client contracts**: `cst_agent_hooks_t` and HTTP/SSE `cst-webui/1` (`hermit --web`)
+
+| Path | Former path | Notes |
+|------|-------------|--------|
+| [`qt-app/`](qt-app/) | `app/` | Qt6/QML GUI (deprecated). Experimental CMake: `-DCST_BUILD_APP=ON`. |
+| [`desktop-tauri/`](desktop-tauri/) | `apps/desktop/` | Tauri 2 + React shell (FFI into `libcstcore`). |
+| [`web-spa/`](web-spa/) | `web/` | Full browser SPA. Load with `hermit --web --web-dev archive/web-spa`. |
+
+**Do not expect** these trees to stay buildable without manual path fixes.
+Default `make` / CI does **not** compile them.
+
+For a new external client, implement against [`docs/webui.md`](../docs/webui.md) and
+[`docs/webui-schema.md`](../docs/webui-schema.md), or embed via `cst_agent.h` hooks / the
+archived FFI bridge under `desktop-tauri/src-tauri/src/ffi_bridge.*`.