Install root dependencies in CI so core/*.ts can resolve SDK

clients/web/tsconfig.app.json's include pulls in ../../core/**/*.ts.
TypeScript module resolution from those files walks up from core/mcp/
looking for node_modules, which lands at the repo root. CI only ran
npm install inside clients/web/, so root node_modules was empty and
core/mcp/types.ts / elicitationCreateMessage.ts / taskNotificationSchemas.ts
failed to resolve @modelcontextprotocol/sdk/types.js and zod/v4
(locally the build worked because root had been manually installed).

Add an explicit root npm install step before the clients/web install.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/main.yml

@@ -16,7 +16,10 @@ jobs:
           node-version: '20.x'
           cache: 'npm'
 
-      - name: Install dependencies
+      - name: Install root dependencies
+        run: npm install
+
+      - name: Install web client dependencies
         working-directory: ./clients/web
         run: npm install