docs(dwh): add ClickHouse source (#16469)

* docs(dwh): add ClickHouse source

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* docs(dwh): remove beta callout from ClickHouse source

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: danielcarletti

contents/docs/cdp/sources/clickhouse.mdx

@@ -0,0 +1,62 @@
+---
+title: Linking ClickHouse as a source
+sidebar: Docs
+showTitle: true
+availability:
+  free: full
+  selfServe: full
+  enterprise: full
+sourceId: ClickHouse
+---
+
+The ClickHouse connector can link your ClickHouse database tables to PostHog. ClickHouse databases are often very large, so we stream the data in Arrow batches to keep memory bounded.
+
+To link ClickHouse:
+
+1. Go to the [Data pipeline page](https://app.posthog.com/data-management/sources) and the sources tab in PostHog
+2. Click **New source** and select ClickHouse
+3. Enter your database connection details:
+    - **Host:** The hostname or IP of your ClickHouse server like `play.clickhouse.com` or `123.132.1.100`.
+    - **Port:** The HTTP(S) port your ClickHouse server is listening on. The default is `8443` for HTTPS and `8123` for HTTP.
+    - **Database:** The name of the database you want to sync. The default is `default`.
+    - **User:** The username with read permissions on the database.
+    - **Password:** The password for the user (optional).
+    - **Use HTTPS?:** Whether to connect over HTTPS. Default is enabled.
+    - **Verify SSL certificate?:** Whether to verify the server's SSL certificate. Default is enabled. Disable if your server uses a self-signed certificate.
+4. If you need to connect through an SSH tunnel, enable and configure it (optional):
+    - **Tunnel host:** The hostname of your SSH server.
+    - **Tunnel port:** The port your SSH server is listening on.
+    - **Authentication type:**
+        - For password authentication, enter your SSH username and password.
+        - For key-based authentication, enter your SSH username, private key, and optional passphrase.
+5. Click **Next**
+
+The data warehouse then starts syncing your ClickHouse data. You can see details and progress in the [sources tab](https://app.posthog.com/data-management/sources).
+
+> **Permissions:** The ClickHouse source only requires read permissions on the database and tables you intend to sync, plus read access to `system.tables` and `system.columns` for schema discovery.
+
+## Supported table engines
+
+PostHog can sync data from any ClickHouse table engine, but row counts are only available for engines that track them:
+
+- **MergeTree family** (including `ReplacingMergeTree`, `SummingMergeTree`, etc.) — full support including accurate row counts from `system.tables.total_rows`.
+- **Distributed tables** — row counts come from a distributed `SELECT count()`.
+- **MaterializedView** — resolves to the underlying `TO` target table or `.inner_id.<uuid>` inner table for row counts.
+- **View** — synced on demand. Row count shown as "Skipped" because counting would require a full scan.
+- **Memory, Buffer, Log, Kafka, URL, and other no-counter engines** — synced on demand. Row count shown as "Skipped".
+
+## Incremental sync
+
+Incremental syncs are supported on integer (`Int8`–`Int256`, `UInt8`–`UInt256`) and temporal (`Date`, `Date32`, `DateTime`, `DateTime64`) cursor fields.
+
+PostHog uses the sorting key from `system.columns` as the detected primary key. Because ClickHouse sorting keys are not guaranteed to be unique, every incremental sync runs a bounded duplicate-key probe first and will fail the sync if duplicates are detected on the chosen primary key.
+
+## Type handling
+
+ClickHouse's Arrow output does not support every type, so PostHog serializes the following to strings on the server side to keep the stream reliable: `UUID`, `IPv4`/`IPv6`, wide ints (`Int128`/`Int256`/`UInt128`/`UInt256`), `Enum8`/`Enum16`, `FixedString`, `Array`, `Map`, `Tuple`, `Nested`, `Variant`, `Dynamic`, `JSON`, and `Object`.
+
+`Nullable` and `LowCardinality` wrappers, `DateTime`/`DateTime64` precision and timezones, and `Decimal[32–256]` are all preserved natively.
+
+import InboundIpAddresses from '../_snippets/inbound-ip-addresses.mdx'
+
+<InboundIpAddresses />