feat(extras): add history + culture domains from corpus mining

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Summary

• Wikipedia 全 dump (4.6GB, 2.4M articles) を dictool candidates corpus で mining し、categorical 分類で 2 新 domain を追加 (history 17件 + culture 18件 = 35件)
• Mozc top-1 と衝突する候補は cost 7000-8000 で常用語を top-1 に維持 (寛保→漢方 / 曹操→早々 / 阿久悠→悪友)
• 既存 Mozc lattice が正解する候補 (徳川家康/三島由紀夫/平家物語/帝国議会/連合国軍最高司令官総司令部 等) は drop

Test plan

• cargo fmt --all --check
• cargo clippy --workspace --all-features -- -D warnings
• cargo test --workspace --all-features
• mise run dict (Merged 'extras': +31 readings, +44 entries, 0 replaced)
• mise run accuracy — 93/93 pass (1 skip 既存)
• mise run accuracy-history — 6/6 pass
• lextool explain で 35 entries 全件 top-1 / cost-conflict 期待値確認

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds two new curated "extras" dictionary domains—history (eras, court ranks, classical works, historical figures) and culture (publishers, music artists, works)—sourced from Wikipedia corpus mining via dictool candidates corpus. Cost overrides (7000–8000) are used for entries that would otherwise displace common-word top-1 results (寛保 vs 漢方, 曹操 vs 早々, 阿久悠 vs 悪友). Accuracy corpus test cases and a unit test in extras.rs verify both the new entries and the cost-conflict coexistence.

Changes:

• Add extras/history.tsv (17 entries) and extras/culture.tsv (18 entries), registered in the DOMAINS list in extras.rs.
• Extend the dict_source::extras::tests smoke test to assert presence of representative history/culture entries and round-tripping of the 寛保 cost override.
• Add 14 accuracy-corpus cases under extras (history/culture/cost-conflict tags) for regression coverage.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
engine/crates/lex-cli/src/dict_source/extras.rs	Register the two new TSVs in DOMAINS and assert representative entries (+ cost override) in tests.
engine/crates/lex-cli/src/dict_source/extras/history.tsv	New curated history vocabulary with selective cost bumps for homophone conflicts.
engine/crates/lex-cli/src/dict_source/extras/culture.tsv	New curated culture/media vocabulary with cost bump for 阿久悠/悪友 conflict.
engine/testcorpus/accuracy-corpus.toml	Add history/culture accuracy cases including cost-conflict coexistence checks.

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.