build: start 0.6.0-SNAPSHOT development

[poppycoderr]

Background

v0.5.0 is tagged. main moves on to the next development version.

Changes

• All modules and the BOM's ddk.version go from 0.5.0-SNAPSHOT to 0.6.0-SNAPSHOT, together with the versions shown in the READMEs and the archetype READMEs.
• CHANGELOG.md gets a new empty [Unreleased] section and its compare link.

-<version>0.5.0-SNAPSHOT</version>
+<version>0.6.0-SNAPSHOT</version>

+## [Unreleased]
+
 ## [0.5.0] - 2026-10-03

---

背景

v0.5.0 已打 tag，main 进入下一个开发版本。

改动

• 所有模块以及 BOM 的 ddk.version 从 0.5.0-SNAPSHOT 改为 0.6.0-SNAPSHOT，README 与两个脚手架 README 里展示的版本号同步修改。
• CHANGELOG.md 新开一个空的 [Unreleased] 一节并补上对比链接（见上文 diff）。