chore: update published SDK dependency

[FanouZeng-TT]

Description

The standalone conformance installation still pins ucp-sdk==0.4.4, while the current published SDK for the same UCP 2026-04-08 release line is 0.4.5:

"ucp-sdk==0.4.4",

CI explicitly runs uv sync --no-sources --no-install-project to validate the published-package path before switching to the editable sibling checkout. Keeping the old pin means that check no longer covers the current published SDK revision.

Fix: update the exact published SDK dependency to 0.4.5. The standalone sync succeeds and all 17 conformance test modules import against that package.

Category (Required)

• Core Protocol: Changes to the base communication layer, global context, or breaking refactors. (Requires Technical Council approval)
• Governance/Contributing: Updates to GOVERNANCE.md, CONTRIBUTING.md, or CODEOWNERS. (Requires Governance Council approval)
• Capability: New schemas (Discovery, Cart, etc.) or extensions. (Requires Maintainer approval)
• Documentation: Updates to README, or documentations regarding schema or capabilities. (Requires Maintainer approval)
• Infrastructure: CI/CD, Linters, or build scripts. (Requires DevOps Maintainer approval)
• Maintenance: Version bumps, lockfile updates, or minor bug fixes. (Requires DevOps Maintainer approval)
• SDK: Language-specific SDK updates and releases. (Requires DevOps Maintainer approval)
• Samples / Conformance: Maintaining samples and the conformance suite. (Requires Maintainer approval)
• UCP Schema: Changes to the ucp-schema tool (resolver, linter, validator). (Requires Maintainer approval)
• Community Health (.github): Updates to templates, workflows, or org-level configs. (Requires DevOps Maintainer approval)

Related Issues

N/A

Checklist

• I have followed the Contributing Guide (including Conventional Commits title requirements and ! for breaking changes).
• I have updated the documentation (if applicable).
• My changes pass all local linting and formatting checks.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• (For Core/Capability) I have included/updated the relevant JSON schemas.
• I have regenerated Python Pydantic models by running generate_models.sh under python_sdk.

Screenshots / Logs (if applicable)

• uv sync --no-sources --no-install-project (resolved ucp-sdk==0.4.5)
• imported all 17 *_test.py modules with --no-sources
• uv run ruff check .
• uv run ruff format --check .
• uvx pre-commit run --all-files
• git diff --check