feat: add Delta Lake connector + docs + test

docs/docs/developers/build/connectors/connectors.md

@@ -211,8 +211,20 @@ Rill is continually evaluating additional OLAP engines that can be added. For a
     linkLabel="Learn more"
     referenceLink="azure"
   />
+</div>
 
+## Table Formats
+### Delta Lake
 
+<div className="connector-icon-grid">
+  <ConnectorIcon
+    icon={<img src="/img/build/connectors/icons/Logo-Delta.svg" alt="Delta Lake" />}
+    header="Delta Lake"
+    content="Read Delta tables directly from object storage through compatible query engines."
+    link="/developers/build/connectors/data-source/delta"
+    linkLabel="Learn more"
+    referenceLink="delta"
+  />
 </div>
 
 ## Table Formats

docs/docs/developers/build/connectors/data-source/data-source.md

@@ -157,6 +157,19 @@ Rill supports connecting your data to both [DuckDB](/developers/build/connectors
 </div>
 
 ## Table Formats
+### Delta Lake
+
+<div className="connector-icon-grid">
+  <ConnectorIcon
+    icon={<img src="/img/build/connectors/icons/Logo-Delta.svg" alt="Delta Lake" />}
+    header="Delta Lake"
+    content="Read Delta tables directly from object storage through compatible query engines."
+    link="/developers/build/connectors/data-source/delta"
+    linkLabel="Learn more"
+    referenceLink="delta"
+  />
+</div>
+
 ### Apache Iceberg
 
 <div className="connector-icon-grid">

docs/docs/developers/build/connectors/data-source/delta.md

@@ -0,0 +1,101 @@
+---
+title: Delta Lake
+description: Read Delta Lake tables from object storage
+sidebar_label: Delta Lake
+sidebar_position: 12
+---
+
+## Overview
+
+[Delta Lake](https://delta.io/) is an open-source storage framework that brings ACID transactions to data lakes. Rill supports reading Delta tables directly from object storage through compatible query engine integrations. Today, this is powered by DuckDB's [Delta extension](https://duckdb.org/docs/stable/core_extensions/delta).
+
+:::note Direct file access only
+Rill reads Delta tables by scanning the table's transaction log and data files directly from object storage. Catalog-based access (e.g., through Unity Catalog) is not currently supported.
+:::
+
+## Storage Backends
+
+Delta tables can be read from any of the following storage backends:
+
+| Backend | URI format | Authentication |
+|---|---|---|
+| Amazon S3 | `s3://bucket/path/to/table` | Requires an [S3 connector](/developers/build/connectors/data-source/s3) |
+| Azure Blob Storage | `azure://container/path/to/table` | Requires an [Azure connector](/developers/build/connectors/data-source/azure) |
+| Local filesystem | `/path/to/table` | No authentication needed |
+
+:::info GCS not yet supported
+Google Cloud Storage is not currently supported for Delta tables. GCS support depends on the upstream DuckDB Delta extension adding it.
+:::
+
+For cloud storage backends, you must first configure the corresponding storage connector with valid credentials. Rill uses these credentials to authenticate when reading the Delta table files.
+
+## Using the UI
+
+1. Click **Add Data** in your Rill project
+2. Select **Delta Lake** as the data source type
+3. Choose your storage backend (S3, Azure, or Local)
+4. Enter the path to your Delta table directory
+5. Enter a model name and click **Create**
+
+For cloud storage backends, the UI will prompt you to set up the corresponding storage connector if one doesn't already exist.
+
+## Manual Configuration
+
+Create a model that uses DuckDB's `delta_scan()` function to read the table.
+
+### Reading from S3
+
+Create `models/delta_data.yaml`:
+
+```yaml
+type: model
+connector: duckdb
+create_secrets_from_connectors: s3
+materialize: true
+
+sql: |
+  SELECT *
+  FROM delta_scan('s3://my-bucket/path/to/delta_table')
+```
+
+### Reading from Azure
+
+```yaml
+type: model
+connector: duckdb
+create_secrets_from_connectors: azure
+materialize: true
+
+sql: |
+  SELECT *
+  FROM delta_scan('azure://my-container/path/to/delta_table')
+```
+
+### Reading from local filesystem
+
+```yaml
+type: model
+connector: duckdb
+materialize: true
+
+sql: |
+  SELECT *
+  FROM delta_scan('/path/to/delta_table')
+```
+
+## Deploy to Rill Cloud
+
+Since Delta tables are read through DuckDB using your existing storage connector credentials, deploying to Rill Cloud follows the same process as the underlying storage connector:
+
+- **S3**: Follow the [S3 deployment guide](/developers/build/connectors/data-source/s3#deploy-to-rill-cloud)
+- **Azure**: Follow the [Azure deployment guide](/developers/build/connectors/data-source/azure#deploy-to-rill-cloud)
+
+Ensure your storage connector credentials are configured in your Rill Cloud project before deploying.
+
+## Limitations
+
+- **Direct file access only**: Rill reads Delta transaction logs and data files directly from storage. Catalog integrations (e.g., Unity Catalog) are not supported.
+- **DuckDB engine**: Delta support is currently provided through DuckDB's Delta extension. Additional engine support is planned.
+- **No GCS support**: Google Cloud Storage is not yet supported by the Delta extension.
+- **Read-only**: Rill reads from Delta tables but does not write to them.
+- **Experimental**: The DuckDB Delta extension is currently marked as experimental.