Python: bump package versions for 1.4.0 release (#5872)

* fixes

* fixes

* Python: bump package versions for 1.4.0 release

Cuts the python-1.4.0 release. MINOR bump on the released cohort
(agent-framework, agent-framework-core, agent-framework-openai,
agent-framework-foundry: 1.3.0 -> 1.4.0), driven by breaking changes
in experimental skills API and new features. All 21 beta packages
stamp 1.0.0b260514, all 3 alpha packages stamp 1.0.0a260514, and
ag-ui remains at 1.0.0rc1 (freshly promoted). Date stamp reflects
2026-05-14 Pacific.

- Released cohort: 1.3.0 -> 1.4.0
- Beta packages (21): 1.0.0b260507 -> 1.0.0b260514
- Alpha packages (3): 1.0.0a260507 -> 1.0.0a260514
- ag-ui: stays at 1.0.0rc1 (dep bound updated only)
- Inter-package dependency lower bounds updated (>=1.3.0 -> >=1.4.0)
- Fix chatkit StructuredInputItem exhaustiveness for openai-chatkit 1.6.4
- Update CHANGELOG compare links
- 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/chatkit/agent_framework_chatkit/_converter.py

@@ -21,6 +21,7 @@ from chatkit.types import (
     HiddenContextItem,
     ImageAttachment,
     SDKHiddenContextItem,
+    StructuredInputItem,
     TaskItem,
     ThreadItem,
     UserMessageItem,
@@ -527,6 +528,9 @@ class ThreadItemConverter:
             case GeneratedImageItem():
                 # TODO(evmattso): Implement generated image handling in a future PR
                 return []
+            case StructuredInputItem():
+                # TODO(evmattso): Implement structured input handling in a future PR
+                return []
             case _:
                 assert_never(item)