chore(docs): update PostgreSQL version requirements

- Update CHANGELOG to document PostgreSQL 14+ as a hard requirement
- Add PostgreSQL version requirements to main README
- Add upgrade warning to Helm chart README for PostgreSQL 13 users

Signed-off-by: Ervin Rácz <ervin.racz@protonmail.com>

Author: ervcz

CHANGELOG.md

@@ -7,6 +7,13 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 ## [Unreleased]
 
 ### Security
+
+## [4.0.0]
+
+### Breaking Changes
+
+- **PostgreSQL 14+ is now a hard requirement:** The `lib/pq` driver has been updated to v1.11.2, which only supports PostgreSQL 14 and newer. Previously, PostgreSQL 17.x was the "tested and default" version, but older versions (e.g., PostgreSQL 13) may have still worked. With this update, **operators running PostgreSQL 13 or older must upgrade their database before upgrading Nebraska**. See the [Upgrade PostgreSQL](https://github.com/flatcar/nebraska/tree/main/charts/nebraska#upgrade-postgresql) migration guide for step-by-step instructions. ([#1300](https://github.com/flatcar/nebraska/pull/1300))
+
 ### Added
 
 - **Multi-Step Updates with Floor Packages:** Added support for mandatory intermediate update versions (floor packages) that clients must install before reaching the target version. This enables safe migration paths for breaking changes by ensuring clients update through specific versions in order. Floor packages can be configured per channel with optional reasons and are architecture-specific. ([#1195](https://github.com/flatcar/nebraska/pull/1195))
@@ -19,6 +26,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
   - Package list UI now updates immediately after blacklist changes
   - Channel edit dialog filters out blacklisted packages from selection
   - Floor package selection prevents choosing blacklisted packages with clear visual feedback
+- Improved reverse domain ID validation regex to eliminate inefficient nested quantifiers flagged by CodeQL, and extracted it into a shared constant with tests. ([#1222](https://github.com/flatcar/nebraska/pull/1222))
 
 ### Removed
 ### Bugfixes

README.md

@@ -15,6 +15,10 @@ Nebraska is an update manager for [Flatcar Container Linux](https://www.flatcar.
 
 [![OpenSSF Scorecard](https://api.scorecard.dev/projects/github.com/flatcar/nebraska/badge)](https://scorecard.dev/viewer/?uri=github.com/flatcar/nebraska)
 
+## Requirements
+
+- **PostgreSQL 14 or newer** (PostgreSQL 17.x recommended)
+
 ## Overview
 
 Nebraska offers an easy way to monitor and manage the rollout of updates to applications that use

charts/nebraska/README.md

@@ -64,6 +64,8 @@ The OIDC implementation has been refactored to use Authorization Code Flow with
 
 ## Upgrade PostgreSQL
 
+> **⚠️ Important:** Nebraska requires **PostgreSQL 14 or newer**. PostgreSQL 17.x is recommended. If you are running PostgreSQL 13 or older, you must upgrade your database before upgrading Nebraska to v4.0.0 or later.
+
 When there is a major upgrade of PostgreSQL, a manual intervention might be required with a downtime. It is possible to automate things with operators, but here's a simple example:
 
 1. Scale down Nebraska deployment: