Python: bump package versions for 1.8.1 release

[Copilot]

Motivation and Context

Cuts the Python 1.8.1 release: version bumps across the workspace, changelog, and inter-package pin alignment.

Description

• Versions: agent-framework (meta), -core, -foundry, -openai 1.8.0 → 1.8.1; dated prereleases bumped for -ag-ui (rc3→rc4), -azurefunctions, -claude, -foundry-hosting, -gemini, -mem0.
• Core pins: aligned each package's agent-framework-core>= lower bound to 1.8.1, per the per-release convention. mem0/claude/gemini/ag-ui skipped the 1.7.0/1.8.0 bumps, so they move >=1.6.0 → >=1.8.1. Refreshed uv.lock.
• Changelog: added the [1.8.1] - 2026-06-09 section; added the [1.8.1] compare link and repointed [Unreleased] to python-1.8.1...HEAD. Removed an incorrect agent-framework-foundry entry for Python: Refactor workflow as agent pending request handling #6259 (that PR only bumped azure-ai-projects; the real fix lives under agent-framework-foundry-hosting).

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? No — release/versioning and changelog only.

[Copilot]

Pull request overview

Bumps the Python workspace package versions for the 1.8.1 release, updates inter-package dependency pins accordingly, refreshes uv.lock, and adds a 1.8.1 changelog entry.

Changes:

• Bump agent-framework (meta), -core, -openai, and -foundry from 1.8.0 → 1.8.1.
• Bump several integration packages to the new dated prerelease versions and update their agent-framework-core minimum versions.
• Refresh python/uv.lock and add a python/CHANGELOG.md entry for 1.8.1 (2026-06-09).

Reviewed changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
python/uv.lock	Updates locked workspace package versions to match the 1.8.1 release set.
python/pyproject.toml	Bumps meta-package version to 1.8.1 and pins agent-framework-core[all] to 1.8.1.
python/packages/core/pyproject.toml	Bumps agent-framework-core version to 1.8.1.
python/packages/openai/pyproject.toml	Bumps agent-framework-openai to 1.8.1 and raises core minimum to >=1.8.1.
python/packages/foundry/pyproject.toml	Bumps agent-framework-foundry to 1.8.1 and aligns core/openai minimums to >=1.8.1.
python/packages/foundry_hosting/pyproject.toml	Bumps agent-framework-foundry-hosting dated alpha version and aligns core minimum to >=1.8.1.
python/packages/azurefunctions/pyproject.toml	Bumps agent-framework-azurefunctions dated beta version and aligns core minimum to >=1.8.1.
python/packages/claude/pyproject.toml	Bumps agent-framework-claude dated beta version and raises core minimum to >=1.8.1.
python/packages/gemini/pyproject.toml	Bumps agent-framework-gemini dated alpha version and raises core minimum to >=1.8.1.
python/packages/mem0/pyproject.toml	Bumps agent-framework-mem0 dated beta version and raises core minimum to >=1.8.1.
python/packages/ag-ui/pyproject.toml	Bumps agent-framework-ag-ui RC version and raises core minimum to >=1.8.1.
python/CHANGELOG.md	Adds the 1.8.1 release section with highlights and referenced PRs.