fix(presigned-url-plugin): use root connection for storage_module queries

[theothersideofgod]

Summary

• Tenant users were getting STORAGE_MODULE_NOT_FOUND because RLS on storage_module checks org_memberships_sprt, which only includes platform users
• Fix: Query storage_module with root connection (pgSettings=null), while keeping bucket/file operations under user RLS
• Pattern matches existing codebase (graphile-i18n, PublicKeySignature)

Security

• databaseId still comes from JWT
• bucket/file RLS unchanged

Test plan

• Provision database with tenant user
• Upload file as tenant user
• Verify file status changes to 'uploaded'

Fixes #1266

🤖 Generated with Claude Code

[theothersideofgod]

Fixed: Remove hardcoded 'public' bucket key

@pyramation Thanks for the review!

Problem: let bucketKey = 'public' as fallback would store files in wrong S3 path

Fix (commit dafc1b72c):

• Require bucketId and lookup key from database
• Return null if not found, falling back to global config
• No more default 'public'

- let bucketKey = 'public';
- if (bucketId) {
-   const bucketResult = await rootClient.query(...);
-   if (bucketResult.rows[0]?.key) {
-     bucketKey = bucketResult.rows[0].key;
-   }
- }
+ if (!bucketId) return null;
+ const bucketResult = await rootClient.query(...);
+ const bucketKey = bucketResult.rows[0]?.key;
+ if (!bucketKey) return null;