feat(changelog): Added a CHANGELOG.md for history

Author: hschimpf

CHANGELOG.md

@@ -0,0 +1,33 @@
+# Changelog
+
+All notable changes to **parallel-sdk** are documented in this file. The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/) and the project adheres to [Semantic Versioning](https://semver.org/).
+
+## `3.0.0` – 2025-07-04
+
+### Added
+- **Domain-specific exception hierarchy**  
+  `ActionNotImplementedException`, `InvalidMessageReceivedException`, `NoWorkerDefinedException`, `TaskExecutionFailedException`, `WorkerAlreadyDefinedException`, `WorkerNotDefinedException`, plus a `ParallelException` value object to serialise task-side errors.
+- `Scheduler::runTask()` now surfaces worker exceptions through `TaskExecutionFailedException` for clearer diagnostics.
+- Adopted modern PHP 8.2 language features:  
+  * `readonly` properties and promoted constructor parameters  
+  * Precise return-type hints (e.g. `void` on closures)  
+  * `match`-style strict comparisons and assorted PSR-12 tidy-ups.
+
+### Changed
+- **BC-BREAK:** Minimum supported PHP version raised from 8.0 → **8.2**.  
+  Consumers on <8.2 will remain on the `2.x` series.
+- `Scheduler::using()` now throws `WorkerAlreadyDefinedException` when attempting to re-register an existing worker with constructor args.
+- Error bubbling in `Scheduler::runTask()` changed from `RuntimeException` with string message to the typed `TaskExecutionFailedException`.
+
+### Removed
+- CI workflows for PHP 8.0 & 8.1 ‒ the suite now runs on 8.2/8.3/8.4.
+- Legacy catch-all `RuntimeException` branches replaced with specific domain exceptions.
+
+### Fixed
+- Sporadic race-condition when starting the runner under PHP ≥ 8.1 by ensuring a micro-sleep and event handshake.
+- Several docblock inaccuracies and progress-bar initialisation edge cases.
+
+---
+
+## [2.1.4] – 2024-xx-xx
+_Refer to Git history for details prior to the 3.x line._