feat(benchmark): expand postgres question set and add results

[jafreck]

Summary

Expands the PostgreSQL benchmark question set from 11 to 15 questions and adds a dedicated results page for the postgres benchmark run.

Changes

Ground truth fixes

• Removed question 3.3 (top-level module dependency map) — the ground truth expected src/backend/* subdirectory-level dependencies, but the question asks for "top-level modules". Both arms answered correctly at the actual top-level granularity (src/port, src/common, src/backend, etc.) but scored 0 because the expected answer was at the wrong level. Neither arm used Lore tools for this question.

New questions (verified against postgres source)

ID	Category	Ground Truth
1.6	Dead code detection	src/backend/parser/analyze.c — all exported functions are called → "None"
2.1	Type hierarchy	TupleTableSlotOps vtable → 4 implementations: TTSOpsVirtual, TTSOpsHeapTuple, TTSOpsMinimalTuple, TTSOpsBufferHeapTuple
3.5	External packages	libxml2 → src/backend/utils/adt, libxslt → contrib/xml2, uuid → contrib/uuid-ossp
5.1	Semantic similarity	Functions similar to heap_insert: heap_update, heap_delete, heap_multi_insert, simple_heap_insert
12.1	Architecture layers	No layering violations → "None"

Benchmark results page

New docs/benchmark-results-postgres.md with full results from a 15-question run:

Metric	Control	Lore	Delta
Mean correctness	69.4%	72.2%	+2.8pp
First-pass accuracy	33.3%	53.3%	+20.0pp
Mean tokens	11,584	3,096	-73.3%
Mean wall time	134.8 s	60.3 s	-55.3%

Biggest wins: task 12.1 (layer violations, -99% tokens) and 1.4 (3-hop blast radius, -95% tokens).

Test results

• 15/15 tasks completed, 14/15 passed
• 1 assertion failure: task 2.1 — both arms scored perfectly but the lore arm used grep instead of any lore_* tool (simple enough for grep on a C struct pattern)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.49%. Comparing base (a564531) to head (eb90133).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

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  Coverage   87.49%   87.49%           
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  Files          85       85           
  Lines        9475     9475           
  Branches     2932     2932           
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  Hits         8290     8290           
  Misses       1185     1185           

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