Python: bump package versions for 1.6.0 release (#6017)

* Python: bump package versions for 1.6.0 release

- Released cohort (agent-framework, core, openai, foundry): 1.5.0 -> 1.6.0
- Beta packages (21 packages): 1.0.0b260519 -> 1.0.0b260521
- Alpha packages (azure-contentunderstanding, foundry-hosting, gemini, monty): 1.0.0a260518/19 -> 1.0.0a260521
- ag-ui stays at 1.0.0rc2, orchestrations at 1.0.0rc1 (dependency bounds updated)
- Inter-package dependency lower bounds updated (>=1.5.0,<2 -> >=1.6.0,<2)
- Update CHANGELOG compare links
- uv.lock refreshed

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Address review: bump RC packages, add shell tool to changelog

- ag-ui: 1.0.0rc2 -> 1.0.0rc3
- orchestrations: 1.0.0rc1 -> 1.0.0rc2
- Add shell tool (#5664) to CHANGELOG
- uv.lock refreshed

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

python/packages/lab/pyproject.toml

@@ -4,7 +4,7 @@ description = "Experimental modules for Microsoft Agent Framework"
 authors = [{ name = "Microsoft", email = "af-support@microsoft.com"}]
 readme = "README.md"
 requires-python = ">=3.10"
-version = "1.0.0b260519"
+version = "1.0.0b260521"
 license-files = ["LICENSE"]
 urls.homepage = "https://aka.ms/agent-framework"
 urls.source = "https://github.com/microsoft/agent-framework/tree/main/python"
@@ -22,7 +22,7 @@ classifiers = [
   "Programming Language :: Python :: 3.14",
 ]
 dependencies = [
-  "agent-framework-core>=1.5.0,<2",
+  "agent-framework-core>=1.6.0,<2",
 ]
 
 [project.optional-dependencies]