fix(studio): disable BFF dynamic tools for workflow roots

[zakahan]

Studio-generated projects with a SequentialAgent, ParallelAgent, or LoopAgent root fail during startup because the generated entry point enables Studio BFF tools while workflow roots have no tools list.

Generate enable_studio_tools=False for these three root types. Also make the shared Runtime configuration disable the channel and log the reason when an existing project explicitly enables it for a workflow root. The capability endpoint reports enabled=False, and no Studio tool execution routes are mounted. LLM roots retain the existing behavior, and child agents retain their configured tools.

Regression coverage includes all three workflow root types, both root_agent and App entry points, enabled/disabled flags, and generated entry-point configuration.

Validation:

• Rebased onto latest upstream/main before committing.
• pre-commit passed (Ruff lint/format and secret scanning).
• pytest -q tests/integrations/agentkit/test_app.py tests/cli/test_generated_agent_backend_codegen_extended.py: 96 passed.