feat(nav): page registry and grouped sidebar (T-I1) - #440

Summary

The app's pages now live in one registry, src/shared/pages/pageRegistry.ts. The sidebar, the page switch, the nav store's Page type and the agent all read it: adding a page is one entry, with no edit to Sidebar.tsx or Router.tsx.

Closes #405

Registry

• Each entry has: id, label, group, icon, load (lazy component) and wrapperClass.
• It's a plain .ts file with icons as data ([tag, attrs]). That way the stores, the agent tools and the node tests (--experimental-strip-types, no JSX) can import it.
• Page is derived from the registry. src/shared/router/routes.tsx is removed.

Sidebar

• Sections in this order: Home, Create, Manage, System, with a separator between them. Groups with no page are skipped.
• Today that gives Create (Generate, Workflows) and System (Extensions, Settings).
• Icons, labels, order and page wrapper classes are identical to before.

Navigation

• navigate(page, params?) opens a page on a target.
• openExtension(id) is now navigate('models', { extension: id }). ModelsPage reads params.extension, then clears it.
• A plain navigate(page) clears stale params.

Agent

• The navigate tool validates the page against the registry.
• The page list (id and label) is sent in the context and rendered as a Pages: line, instead of a fixed enum in agent.py.
• Values are capped and kept on one line.

Test plan

• npm run test:node: 259 tests, 258 pass, 0 fail. New tests: pageRegistry.test.ts (registry, grouping, navigate/openExtension).
• python -m unittest tests.test_agent_client_tools: OK. The pre-push hook ran the full suite.
• ESLint is clean. tsc reports no new errors.
• npm run build passes, and each page is still its own chunk.
• Manual:
  • The sidebar shows two groups with a separator, and each page opens as before.
  • From a workflow node or the Generate workflow panel, "open extension" lands on Extensions with that extension selected. Try it twice, and once from the Extensions page itself.
  • In the agent panel, "Va sur les réglages" opens Settings.