fix(send-email-link): use X-Meta-Schema for platform data queries

## Problem

send-email-link fails for newly provisioned databases (e.g., kanban, crm)
with the error:

  Cannot query field "databases" on type "Query"

However, it works correctly for the `constructive` database.

## Root Cause

send-email-link queries platform-level data (databases, sites, domains,
siteThemes, siteModules) using `X-Api-Name: private` header. This relies
on the database's `private` API having access to meta schemas.

The issue is:
- `constructive` database: private API includes meta schemas (seed data)
- New databases (kanban, crm): private API does NOT include meta schemas

The `private` API's accessible schemas are determined by the
`services_public.api_schemas` table. For `constructive`, this was
manually configured to include `metaschema_public` and `services_public`.
But the provision flow does not add these meta schemas for new databases.

## Analysis

GetDatabaseInfo query needs:
- `databases` table (metaschema_public)
- `sites`, `domains`, `siteThemes`, `siteModules` tables (services_public)

These are platform-level data, not per-database business data. They should
be accessed via `X-Meta-Schema: true` header, which directly exposes the
meta schemas regardless of which database is being queried.

## Solution

Change the `meta` GraphQL client to use `useMetaSchema: true` instead
of `X-Api-Name: private`. This ensures:

1. Platform data is always accessible via X-Meta-Schema header
2. No dependency on per-database API configuration
3. Works for all databases (existing and new)

The `client` (for GetUser query) still uses `X-Api-Name: private` since
it needs per-database user data.

## Before

```typescript
const meta = createGraphQLClient(metaGraphqlUrl, {
  databaseId,
  ...(apiName && { apiName }),  // X-Api-Name: private
});
```

## After

```typescript
const meta = createGraphQLClient(metaGraphqlUrl, {
  useMetaSchema: true,  // X-Meta-Schema: true
});
```

## Testing

Verified with:
- constructive database: ✅ email sent successfully
- kanban database: ✅ email sent successfully (was failing before)

Author: theothersideofgod

functions/send-email-link/src/index.ts

@@ -361,13 +361,11 @@ app.post('/', async (req: any, res: any, next: any) => {
       ...(schemata && { schemata }),
     });
 
-    // For GetDatabaseInfo query - uses same API routing as client
-    // The private API exposes both user and database queries
+    // For GetDatabaseInfo query - uses X-Meta-Schema to access platform data
+    // (databases, sites, domains, siteThemes, siteModules are platform-level data)
     const meta = createGraphQLClient(metaGraphqlUrl, {
       hostHeaderEnvVar: 'META_GRAPHQL_HOST_HEADER',
-      databaseId,
-      ...(apiName && { apiName }),
-      ...(schemata && { schemata }),
+      useMetaSchema: true,
     });
 
     const result = await sendEmailLink(params, {