feat(07-01): extend FieldDef with validate/tooltipText and add 3 validate rules

- Add validate?: { regex: RegExp; message: string } to FieldDef interface
- Add tooltipText?: string to FieldDef interface (prep for Plan 07-02)
- Add validate rule to azureblob.account: /^[a-z0-9]{3,24}$/
- Add validate rule to s3.region: /^[a-z][a-z0-9-]+[a-z0-9]$/
- Add validate rule to gcs.project_number: /^\d+$/

src/schemas/registry.ts

@@ -14,6 +14,8 @@ export interface FieldDef {
   placeholder?: string;
   helpText?: string;
   options?: { value: string; label: string }[]; // for inputType: 'select'
+  validate?: { regex: RegExp; message: string };
+  tooltipText?: string;
 }
 
 export const BACKEND_REGISTRY = {
@@ -28,6 +30,10 @@ export const BACKEND_REGISTRY = {
         required: true,
         placeholder: 'mystorageaccount',
         helpText: 'The storage account name (not the full URL)',
+        validate: {
+          regex: /^[a-z0-9]{3,24}$/,
+          message: 'Must be 3–24 lowercase alphanumeric characters (no hyphens or uppercase)',
+        },
       },
       {
         key: 'key',
@@ -76,6 +82,10 @@ export const BACKEND_REGISTRY = {
         inputType: 'text',
         required: true,
         placeholder: 'us-east-1',
+        validate: {
+          regex: /^[a-z][a-z0-9-]+[a-z0-9]$/,
+          message: 'Must be a valid AWS region format (e.g. us-east-1)',
+        },
       },
     ],
   },
@@ -166,6 +176,10 @@ export const BACKEND_REGISTRY = {
         required: true,
         placeholder: '123456789',
         helpText: 'Your GCP project number (not project ID)',
+        validate: {
+          regex: /^\d+$/,
+          message: 'Must contain digits only',
+        },
       },
       {
         key: 'service_account_credentials',