fix(loader): use consistent key for retrieval tools in collect_classes

[MicaPerdomo]

Summary

collect_classes stores retrieval tool entries using obj.__name__ (e.g. "ProductDocsSearch"), but collect_definitions uses the explicit name attribute (e.g. "product_docs_search"). When the migration runner looks up classes by definition key, the mismatch causes "retrieval is required for retrieval tool" errors.

This changes collect_classes to use getattr(obj, "name", None) or obj.__name__ as the key, matching the logic already used in collect_definitions.

Changes

• cogsol/core/loader.py: Use consistent key logic in collect_classes for retrieval tools (1 line → 2 lines)
• tests/test_agents.py: Add 2 tests for explicit name keying and fallback behavior

Test plan

• pytest — all tests pass (94 total, 2 new)
• black --check . — no formatting changes
• ruff check . — 0 errors
• mypy cogsol — 0 issues

[MicaPerdomo]

Closing — these changes are already included in #10.