Enable Ruff TRY003 by removing inline exception messages

[Copilot]

This removes the global TRY003 suppression from Ruff and brings the existing exception-raising code into compliance. The change preserves current exception types and message text while eliminating inline message construction at raise sites.

• What changed

  • Removed TRY003 from the Ruff ignore list in pyproject.toml.
  • Added a small shared helper for constructing exceptions from message strings.
  • Replaced existing raise SomeError("...") / raise SomeError(f"...") patterns across the Python codebase with helper-based construction.

• Why this shape

  • Keeps the change mechanical and low-risk.
  • Avoids introducing a large number of one-off exception subclasses solely to satisfy the lint rule.
  • Preserves current runtime behavior and error text.

• New shared pattern

  from seclab_taskflow_agent.error_utils import error_with_message
  
  raise error_with_message(
      BackendTimeoutError,
      f"Backend stream idle for {STREAM_IDLE_TIMEOUT}s",
  )

• Scope of refactor

  • Runner and stream handling
  • YAML/resource loading
  • MCP transport/lifecycle utilities
  • CodeQL MCP server/client helpers
  • CLI, session, template, and SDK backend validation paths

• Supporting changes

  • Added a focused unit test for the new exception-construction helper.