feat(presigned-url): add per-bucket mutation entry points on root Mutation type

[pyramation]

Summary

Adds per-bucket mutation fields on the root GraphQL Mutation type so that upload operations (requestUploadUrl, requestBulkUploadUrls) can be accessed as proper mutations instead of queries. Previously, these were only reachable via query fields on bucket types.

For each @storageBuckets-tagged codec, the plugin now adds a mutation field named after the bucket type (e.g., appBucket, dataRoomBucket):

mutation {
  appBucket(key: "public") {
    requestUploadUrl(contentHash: "...", contentType: "...", size: 123) {
      uploadUrl fileId key deduplicated expiresAt
    }
  }
}

Entity-scoped buckets automatically include a required ownerId argument. The mutation resolves the bucket row via getBucketConfig and returns an ObjectStep with access() steps for each codec attribute, so existing sub-field plans (which call $parent.get('column')) continue to work.

Review & Testing Checklist for Human

• ObjectStep ↔ PgSelectSingleStep compatibility: The mutation plan returns a Grafast object() step, NOT a PgSelectSingleStep. PostGraphile's generated attribute field plans call $parent.get('column') — verify that ObjectStep.get() behaves identically to PgSelectSingleStep.get() for sub-field resolution. This is the highest-risk area and has not been integration-tested.
• Column coverage gap: getBucketConfig returns only 8 fields (id, key, type, is_public, owner_id, allowed_mime_types, max_file_size, allow_custom_keys), but the object() step is built from Object.keys(codec.attributes) which may include additional columns (e.g., created_at). Selecting those columns through the mutation entry point will return undefined. Verify this is acceptable or if SELECT * should be used instead.
• Integration test: Run the minio-multi-scope integration test in constructive-db with a mutation { appBucket(...) { requestUploadUrl(...) { ... } } } query to confirm the full plan chain resolves correctly at runtime.

Notes

• The @pgpmjs/logger type errors in the build output are pre-existing on main (verified by building before and after changes). The workspace-level pnpm build passes cleanly.
• ownerId uses GraphQLString rather than the PostGraphile UUID scalar — works but is less type-precise.
• Related: this unblocks updating the failing test in constructive-db PR #1054 to use the mutation API.

Link to Devin session: https://app.devin.ai/sessions/7903d2a3e7a34c6daa605e12d6b80d9e
Requested by: @pyramation

[devin-ai-integration]

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