test: add unicode press() regression tests for umlaut and CJK characters

[Kartalops]

Summary

• Add 3 regression tests for press() with unicode characters (German umlauts, CJK, SHIFT+unicode)
• Test_press.py previously only covered ASCII characters (a-z, A-Z)

Problem

tests/api/test_press.py had only ASCII test coverage. No test verified that press() correctly handles unicode input via Selenium's send_keys(). This is a regression gap — unicode support exists in the implementation but has no test.

Solution

Add 3 targeted regression tests:

• test_press_unicode_german_umlaut: verify 'ü' works
• test_press_unicode_chinese: verify '中' works
• test_press_unicode_combined: verify SHIFT+'ü' doesn't throw

Tests

# Chrome (default)
python setup.py test

# Firefox
TEST_BROWSER=firefox python setup.py test

All tests run against test_write.html (Autofocus text field).

Risk / Compatibility

• Risk: LOW — test-only change, no production code modified
• Affects: tests only (test_press.py)
• No public API changes
• No new dependencies

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