feat(17-03): create CreateInitiativeDialog with shadcn primitives

- Install shadcn Dialog, Input, Label, Textarea components
- Move from @/ literal dir to src/components/ui/ (known shadcn CLI issue)
- CreateInitiativeDialog: controlled dialog with name/description fields
- tRPC createInitiative mutation with loading/error states
- Form resets on open, validates name non-empty

packages/web/package.json

@@ -11,6 +11,8 @@
   },
   "dependencies": {
     "@codewalk-district/shared": "*",
+    "@radix-ui/react-dialog": "^1.1.15",
+    "@radix-ui/react-label": "^2.1.8",
     "@tanstack/react-query": "^5.75.0",
     "@tanstack/react-router": "^1.158.0",
     "@trpc/client": "^11.9.0",