Wire gnexus-ui-kit v0.2.0 Vue 3 adapter and migrate Wave 1 components. ...

- Update vendor/gnexus-ui-kit to v0.2.0 (Vue components + composables)
- Add Vite aliases for gnexus-ui-kit/vue and gnexus-ui-kit/css
- Install GnexusUiVue plugin in main.js + GnToastProvider in App.vue
- Migrate ProfileBadge → GnBadge
- Migrate ErrorMessage → GnAlert
- Migrate ConfirmDialog → GnConfirmDialog
- Migrate raw <button> elements → GnButton / GnIconButton in:
  WelcomeScreen, LoginScreen, ChatArea, ChatHeader, AppSidebar,
  ArtifactsPanel, UserMessage, AssistantMessage, SelectionToolbar

Build and tests pass (51/51).

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

Remove erroneous vue-router from webclient ...

vue-router was accidentally left over from an earlier attempt to embed
admin features in the main client. It broke hash-based session routing
and rendered app-main empty. Revert to direct component rendering in
App.vue with native hashchange handling.

- Remove vue-router dependency and src/router/index.js
- Revert main.js to createApp without router
- App.vue: render WelcomeScreen/ChatArea directly, restore hashchange handler
- chat.js: revert hash format to raw session id
- api/index.js: keep 401 → authStore.user = null (login overlay fix)

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

Add pagination, search, and sorting to admin sessions ...

Backend:
- Add count_all and search_list abstract methods to SessionStore
- Implement count_all and search_list in PgSessionStore (SQL with ILIKE)
- Implement count_all and search_list in InMemorySessionStore
- Update /admin/sessions to accept limit, offset, search, sort_by, sort_order
- Return {total, limit, offset, items} from /admin/sessions

Frontend:
- Add search input for sessions in admin panel
- Add clickable sortable column headers with asc/desc toggle
- Add pagination controls (prev/next, page size selector, item count)
- Debounce search input (300ms)

Tests:
- Add integration tests for pagination, offset, search, and sorting
- All 217 tests pass

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

Migrate to Vue webclient; rename old client to old_webclient ...

- client/ → old_webclient/ (vanilla JS client preserved as reference)
- webclient/ — new Vue 3 + Pinia webclient (source + dist build)
- vite.config.js: outDir changed to webclient/dist/
- main.py: serve /assets and /images from webclient/dist/,
  index.html from webclient/dist/index.html
- .gitignore: exclude webclient/node_modules/, include webclient/dist/

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>