Add ruff lint, format, and mypy checks for agent service in CI

[0vertake]

The agent service has ruff and mypy configured in pyproject.toml but these checks are not enforced in CI.

Current state:

• Unit tests run in CI via the "Agent Tests" Semaphore block
• ruff (lint + format) and mypy (typecheck) are configured in pyproject.toml but the codebase doesn't pass any of them

What needs to happen:

• Fix all ruff lint violations
• Fix all ruff format violations
• Fix all mypy strict mode errors
• Add Makefile targets in agent/Makefile for lint, format check, and typecheck
• Add CI jobs for all three checks in the Agent Tests Semaphore block