docs: add PostgreSQL 12→18 breaking change notice and link from Docker page

Author: deepesh-np

content/docs/install/docker.mdx

@@ -87,4 +87,11 @@ The next step is to learn how to use LogChimp.
 
 - LogChimp Docker images:
 - APIs - [link](https://github.com/orgs/logchimp/packages/container/package/logchimp%2Fapi)
-- Theme - [link](https://github.com/orgs/logchimp/packages/container/package/logchimp%2Ftheme)
+- Theme - [link](https://github.com/orgs/logchimp/packages/container/package/logchimp%2Ftheme)	
+
+<Alert type="warning">
+	⚠️ **Breaking Change (PostgreSQL 12 → 18)**  
+	LogChimp now uses PostgreSQL 18 which introduces an incompatible data directory structure.  
+	Existing Docker volumes or databases from PostgreSQL 12 **will not work directly** with this version.  
+	Please review the [Breaking Change – PostgreSQL 12 → 18](/docs/miscellaneous/breaking-changes-pg18) page before upgrading or deploying.
+</Alert>																																																																																																																																																																																																																																																																																

content/docs/install/railway.mdx

@@ -13,6 +13,13 @@ There are many ways to [install LogChimp](/docs/install/getting-started). With R
 	notifications and more.
 </Alert>
 
+<Alert type="warning">
+	⚠️ **Breaking Change (PostgreSQL 12 → 18)**  
+	LogChimp now uses PostgreSQL 18 which introduces an incompatible data directory structure.  
+	Existing Docker volumes or databases from PostgreSQL 12 **will not work directly** with this version.  
+	Please review the [Breaking Change – PostgreSQL 12 → 18](/docs/miscellaneous/breaking-changes-pg18) page before upgrading or deploying.
+</Alert>
+
 [![Deploy on Railway](https://railway.app/button.svg)](https://railway.app/new/template/3Bm-Un?referralCode=mittalyashu)
 
 All the environment variables are pre-configured for you. You can learn more about them [here](/docs/environment-variables).

content/docs/install/render.mdx

@@ -13,6 +13,13 @@ Clicking the "Deploy to Render" button will redirect you to the Render blueprint
 	notifications and more.
 </Alert>
 
+<Alert type="warning">
+	⚠️ **Breaking Change (PostgreSQL 12 → 18)**  
+	LogChimp now uses PostgreSQL 18 which introduces an incompatible data directory structure.  
+	Existing Docker volumes or databases from PostgreSQL 12 **will not work directly** with this version.  
+	Please review the [Breaking Change – PostgreSQL 12 → 18](/docs/miscellaneous/breaking-changes-pg18) page before upgrading or deploying.
+</Alert>
+
 All the environment variables are pre-configured for you. You can learn more about them [here](/docs/environment-variables).
 
 [![Deploy to Render](https://render.com/images/deploy-to-render-button.svg)](https://render.com/deploy?repo=https://github.com/logchimp/deploy-buttons)

content/docs/meta.json

@@ -13,7 +13,8 @@
     "---Miscellaneous---",
     "[HandHelping][Contributing](https://github.com/logchimp/logchimp/blob/master/CONTRIBUTING.md)",
     "miscellaneous/faq",
-    "miscellaneous/security-policy"
+    "miscellaneous/security-policy",
+    "miscellaneous/breaking-changes-pg18"
   ],
   "defaultOpen": true
 }

content/docs/miscellaneous/breaking-changes-pg18.mdx

@@ -0,0 +1,25 @@
+## Breaking Changes: PostgreSQL 12 → 18
+
+<Alert type="warning">
+	⚠️ **Important Notice:**  
+	Upgrading to PostgreSQL 18 introduces a new cluster storage layout that is **not compatible** with PostgreSQL 12.  
+	Existing Docker volumes or data directories from v12 **will fail to start** unless properly migrated.  
+	Please back up your data and follow the steps below before proceeding with any upgrade.
+</Alert>
+
+## Summary
+PostgreSQL 18 introduces a new cluster storage layout incompatible with version 12.
+
+## Impact
+- Existing Docker volumes from v12 will fail to mount directly.  
+- `pg_upgrade` or data export/import is required.  
+- Environment variables and data paths differ (`/var/lib/postgresql/18/data`).
+
+## Recommended Action
+1. Backup all data from v12.  
+2. Use the official upgrade container or `pg_upgrade`.  
+3. Verify compatibility in staging before production rollout.
+
+## References
+- [PostgreSQL Docker Migration Notes](https://github.com/docker-library/postgres/pull/1259)  
+- [Official PostgreSQL Upgrade Guide](https://www.postgresql.org/docs/18/pgupgrade.html)