feat(agent): add document skills and shared Python environment

[Patodo]

Changes

Applications can select Server-provided PDF, DOCX, XLSX and MarkItDown skills and control available tools per user. The settings use shared shadcn/ui components and expose application tools before the first Agent request.

Administrators can select an existing Python virtual environment or create one for all Agent scripts, install document dependencies, and inspect readiness in System Settings. Checks and execution use the same interpreter. Skills with missing dependencies cannot be enabled; the shared environment is read-only during Agent execution.

Includes bundled skill sources, licenses, packaging and documentation. Chat attachment upload and image input are outside this change; document verification uses files already in the Agent workspace.

Validation

• Focused Server environment, sandbox and permission integration tests passed (21 tests).
• Web settings tests, Server type checking and production Web build passed.
• Packaged Node Server and public source export checks passed.
• Local end-to-end verification created a Python 3.12 environment and used a real model to invoke the PDF skill and extract the expected page count and text.
• Earlier full Server and Web suites passed; CI will run the complete suite for this final commit.