chore(forms): remove unused vee-validate; formalize ref+validators+Zod as canonical pattern

Strict-regex sweep of apps/app/src/ confirms zero VeeValidate usage:
no `from 'vee-validate'` imports, no <Field|Form|ErrorMessage>,
no defineRule(), no useForm(). The 15 prior fuzzy matches were
false positives where /useForm/ matched useFormDraft/useFormSteps/
useFormSchemas/useFormFailures.

Changes:
- Remove `vee-validate` and `@vee-validate/zod` from apps/app/package.json
- Regenerate pnpm-lock.yaml (no other deps shifted)
- CLAUDE.md "Forms": replace VeeValidate prescription with the actual
  ref + @core/utils/validators + Zod-payload-schema pattern that the
  codebase already uses everywhere
- VUEXY_COMPONENTS.md: correct the stale "Registration uses VeeValidate"
  claim (the page actually uses useFormDraft + validators); update the
  "Form validation" reference row
- BACKLOG.md: close VEE-001 with the audit trail

All 319 existing tests still pass; vue-tsc clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/app/package.json

@@ -30,7 +30,6 @@
     "@tiptap/pm": "^2.27.1",
     "@tiptap/starter-kit": "^2.27.1",
     "@tiptap/vue-3": "^2.27.1",
-    "@vee-validate/zod": "^4.15.1",
     "@vueuse/core": "10.11.1",
     "@vueuse/math": "10.11.1",
     "apexcharts": "3.54.1",
@@ -50,7 +49,6 @@
     "shepherd.js": "13.0.3",
     "ufo": "1.6.1",
     "unplugin-vue-define-options": "1.5.5",
-    "vee-validate": "^4.15.1",
     "vue": "3.5.22",
     "vue-chartjs": "5.3.2",
     "vue-flatpickr-component": "11.0.5",