feat(config): add manager term overlays

[TATP-233]

Summary

• add explicit dataclass metadata for Manager-Based term and parameter mappings
• overlay only factory-owned manager/group/term fields while preserving callables, sibling terms, nested dataclass parameters, and insertion order
• treat null / None as term disablement and fail closed for unknown terms, disabled-term enablement, raw replacement, or func overrides
• preserve the registry's existing replacement semantics for ordinary unmarked dictionaries

Implements #1068.
Part of #1042.

Scope accounting

• source-derived code: 0 lines
• mechanical changes: dataclass metadata plumbing only (about 30 lines)
• UniLab-specific implementation/glue: about 150 added lines
• tests: 165 added lines
• files changed: 6

Validation

• uv run pytest tests/base/test_manager_config_overlay.py -q: 8 passed
• broader manager suite: 107 passed
• make test-all:
  • ruff, mypy, pyright passed
  • pytest: 1921 passed, 25 skipped, 274 deselected, 1 xfailed
  • benchmark module mode: 32/33 passed, 1 platform-optional skip
  • benchmark script mode: 33/34 passed, 1 platform-optional skip