Add Dayi smart candidate selection

[omni624562]

Summary / 摘要

中文

新增大易智慧選字，依使用者實際選字記錄調整候選字排序。

主要內容：

• 大易候選字會依選字次數排序
• 支援近期選字加權
• 支援前一字上下文加權
• cincount.json 支援舊格式相容與壞資料容錯
• 每個候選字最多保留 32 筆前文上下文，避免長期使用資料無限成長
• 寫檔有 60 秒節流，停用/釋放時強制保存
• 大易設定頁加入智慧選字、近期優先、前一字上下文加權開關
• 新增測試涵蓋資料格式、排序、上下文上限與寫檔節流

English

Adds smart candidate selection for Dayi by learning from the user's actual candidate choices.

Highlights:

• Reorders Dayi candidates by learned selection frequency
• Supports recency weighting
• Supports previous-character context weighting
• Keeps compatibility with older cincount.json formats and tolerates malformed entries
• Caps previous-context data at 32 entries per candidate to avoid unbounded long-term growth
• Throttles writes to once per 60 seconds, with forced save on deactivation/destruction
• Adds Dayi settings for smart selection, recency weighting, and previous-context weighting
• Adds tests for data normalization, sorting, context caps, and save throttling

Validation / 驗證

• git diff --check
• python -m py_compile python\cinbase\__init__.py python\cinbase\cin.py python\cinbase\config.py python\cinbase\configtool.py python\server.py
• python -m unittest tests.test_backend_resilience