Remove fragile heuristic abstractions from review pipeline

Delete ConfidenceFilter (dedup, FP heuristics, category thresholds),
judge_issues LLM call, and dead reviewer methods (_cross_file_dedup,
_issues_same, _llm_aggregate, _default_review_instructions,
_default_judge_prompt, dead Pydantic models). The agentic review
prompt handles all of this directly.