Add observation profiles for source coverage

[DavidJBianco]

Summary

• Adds source identity and endpoint baseline realism updates from the current stacked branch.
• Adds overlay-compatible observation profiles with a training-friendly complete default plus non-default partial-collection profiles.
• Records source evidence status in ground truth while keeping canonical truth deterministic.

Verification

• uv run eforge validate-config
• uv run ruff check .
• uv run ruff format --check .
• uv run pytest -v
• uv run pytest -v --include-slow

Notes

• This PR is intentionally opened before continuing the larger Sprint 4 host-activity distribution work so the observation-profile branch stays visible and reviewable.