Improve consistency of uv use in worfklows

[ahouseholder]

This PR

• replaces pip install -r requirements.txt with uv sync... and ensures that the deploy_site.yml workflow functions as intended.
• fixes broken soft links in data/schema/current that changed with PR Refactor JSON schema generation for consistency #946
• adds soft links from old file names in data/schema/v2 that changed in PR Refactor JSON schema generation for consistency #946
• adds data/schema/v2/README.md to explain the links

This branch has already been confirmed to work in https://github.com/CERTCC/SSVC-staging/actions/runs/17676879600

Copilot Summary

This pull request updates the schema file naming conventions and improves dependency management in the GitHub workflow files. The main changes include switching to new schema filenames with soft links for backward compatibility, updating workflow steps to use the uv package manager, and ensuring workflows are triggered on changes to the new dependency file.

Schema file updates and migration:

• Updated references in data/schema/current/*.schema.json to point to new schema filenames (e.g., DecisionPoint_2_0_0.schema.json, SelectionList_2_0_0.schema.json) for improved consistency. [1] [2] [3]
• Added new schema files and soft links in data/schema/v2/ to map old names to new ones, supporting a smoother transition. [1] [2] [3] [4] [5]
• Added a README.md to explain the rationale for the soft links and the automated schema generation process.

Workflow and dependency management improvements:

• Updated .github/workflows/deploy_site.yml and .github/workflows/link_checker.yml to use the uv package manager for dependency installation and site building, replacing direct pip and mkdocs calls for better reliability and reproducibility. [1] [2]
• Modified workflow triggers to include changes to src/pyproject.toml, ensuring CI runs when dependencies are updated in the new format.
• Streamlined dependency installation in .github/workflows/python-app.yml to use uv consistently and removed commented-out legacy pip commands.

[sei-vsarvepalli]

See related discussion #947 - we should announce to others who may be trying to use the schema. I will add it to CSAF 2.1 candidate too.