fix(tests): make dtu tool-composition test portable and collection-safe

[colombod]

✅ Delivered — merged to main. Related: #29 (the graph-query params/docs work this was split out from).

Problem

tests/dtu/test_tool_delegate_composition.py hardcoded an absolute, root-owned cache path and ran its checks at import time:

cache = Path("/root/.amplifier/cache/amplifier-bundle-context-intelligence-ecd41f3e6fa67bd2")
...
facilitator_fm, _ = load_frontmatter("agents/...")   # module-level
...
sys.exit(1)                                            # module-level on failure

On any environment other than that exact DTU container this raised PermissionError: [Errno 13] Permission denied: '/root/.amplifier/cache/...' during pytest collection, which aborted collection for the whole tests/ tree (1 error, 0 tests run from the top-level suite).

Fix

• Resolve the bundle root relative to the test file: BUNDLE_ROOT = Path(__file__).resolve().parents[2]. The agent and mode files under test (agents/context-intelligence-design-facilitator.md, agents/context-intelligence-tool-designer.md, modes/context-intelligence.md) ship in this repo, so the repo root is the correct, portable source — works in a checkout, in CI, and inside a DTU alike.
• Move the validation into a real def test_tool_delegate_composition() that asserts on failures instead of sys.exit(1), so collection no longer executes the body. Retained an if __name__ == "__main__" runner so the file still works as a standalone DTU script. All 14 Group-D checks are unchanged.

Test Plan

• tests/dtu/test_tool_delegate_composition.py: 1 passed (was a collection error)
• Full top-level suite now collects and runs clean: 657 passed (previously aborted at collection)
• ruff lint + format clean