fix(consolidation): preserve source language in observations

[oldnicke]

Summary

• require consolidation CREATE and UPDATE actions to follow the dominant language of their referenced new facts when no output language override is configured
• validate generated observation language, issue one schema-preserving corrective retry, and apply a configurable fail-batch or fail-open policy
• add privacy-safe diagnostics, configuration documentation, deterministic regression coverage, and a real-model judge test

Test plan

• ./scripts/hooks/lint.sh
• uv run pytest tests/test_consolidation_language.py tests/test_consolidation_retry_budget.py tests/test_multilingual_bm25.py tests/test_config_validation.py tests/test_prompt_brace_escape.py -m "not hs_llm_core" -q (154 passed)
• uv run pytest tests/test_consolidation.py -m "not hs_llm_core" -q (63 passed)
• ./scripts/hooks/check-unused.sh (advisory checks completed; no new findings)

Fixes #3166