[stantheman0128]

Closes #984.

Problem

Simplified 冲 merges two traditional characters: 沖 (rinse / flush / brew) and 衝 (charge / collide / impulse). On current master, STCharacters.txt prefers 衝:

冲	衝 沖

That makes unmatched 冲 convert to 衝, which is wrong for everyday rinse/brew uses such as 冲咖啡. Issue #984 was retitled from 冲 --> 衝 to 冲 --> 沖 (衝), asking for 沖 as the default candidate and 衝 as the non-default alternative. Phrase-level 衝 senses are already covered in STPhrases.txt (for example 水一冲 -> 水一衝, 冲突 -> 衝突).

Change

• STCharacters.txt: swap the s2t candidate order for 冲 from 衝 沖 to 沖 衝, following CONTRIBUTING.md (keep the old conversion as a non-default candidate) and the precedent of s2t: fix 托/託 candidate priority so 托 stays unconverted by default #1405.
• testcases.json: add BYVoid_OpenCC_Issue_984_chong_variant_priority covering default 沖 uses, the issue example 清水一冲 -> 清水一衝, and common 衝 compounds.

No STPhrases.txt edits were required; existing phrase entries already pin the 衝 senses.

Verification

I had no C++ toolchain available, so I verified with the OpenCC 1.4.1 wheel engine driving this branch's text dictionaries directly: config JSONs identical to data/config/*.json with ocd2 references switched to text. There are no conversion related engine changes between ver.1.4.1 and master for this character mapping. A/B against master dictionaries with the same harness:

new Issue_984 testcase on master dictionaries:  FAIL (冲咖啡 -> 衝咖啡)
new Issue_984 testcase on this branch:          PASS (冲咖啡 -> 沖咖啡; 清水一冲 -> 清水一衝)
existing testcases.json expectations A/B:       same 462 pass / 31 fail on both
                                                (the 31 fails are from omitted generated
                                                regional/rev dictionaries in the local
                                                text harness, not from this diff)
sort.py on STCharacters.txt:                    mapping remains 冲<TAB>沖 衝

Sample before/after (s2t; base = master, mod = this branch):

冲                          base=衝            mod=沖
冲咖啡                      base=衝咖啡        mod=沖咖啡
冲洗                        base=沖洗          mod=沖洗
清水一冲                    base=清水一衝      mod=清水一衝
再用清水一冲就能清除了      base=再用清水一衝就能清除了  mod=再用清水一衝就能清除了
冲突                        base=衝突          mod=衝突
冲动                        base=衝動          mod=衝動
冲锋                        base=衝鋒          mod=衝鋒
缓冲                        base=緩衝          mod=緩衝
兴冲冲                      base=興沖沖        mod=興沖沖

Please treat the CI Bazel dictionary tests as the authoritative check.

This fix was developed with AI assistance (Cursor/Grok) and verified locally as shown above.