Add test suite (45 tests) + GitHub Actions CI

[ltsuemitsu]

Phase 3 foundation: tests + CI

The project had zero tests — every change (like the 4 PRs we just merged) was verified by hand. This adds the safety net.

Test suite — 45 tests, stdlib unittest only (no pytest needed)

File	Tests	Covers
tests/test_tradutor.py	24	TagProtector protect/restore round-trip (game markup {g|…}, <color>, <sprite>, <link>), SmartGlossary preserve logic (flags, categories, complete vs preserve mode, exact/contains matching), split_batch token cap, blacklist loading, atomic_save
tests/test_diff_tool.py	7	detect_update patch deltas, audit_translation untranslated detection, smart_diff
tests/test_merge.py	4	merge + backup, validator guard, dry-run
tests/test_glossary_wiki.py	10	GlossaryEntry round-trip, load/save, wiki dataset integrity (16 categories / 2,694 terms)

• Runs with python -m unittest discover -s tests -v — currently 45/45 green ✅
• Zero network, zero API keys; fixtures are tiny synthetic Owlcat JSONs in temp dirs

CI — .github/workflows/tests.yml

• Push + PR on main
• Matrix: ubuntu + windows × Python 3.10 + 3.12 (3.10 guards against the PEP-701 regression class from [BUG] wiki_sync.py is a SyntaxError on Python < 3.12 #3)
• compileall syntax gate → unittest

README

CI badge + Development section with test instructions.

Notes

• Tests documented three real engine behaviors worth knowing (not bugs): contains-match only runs for texts >15 chars; hyphen↔space variant is one-directional; merge's validator guard refuses only when all items are untranslated.
• GUI (tradutor_desktop.py) intentionally not in CI scope (PySide6 excluded); core engine is fully covered.

After merge, every future PR gets an automatic green/red check.