Handle Unicode-unsafe terminals in CLI success output

[srichs]

Motivation

• The CLI emitted emoji-only success messages which raised UnicodeEncodeError on terminals that can't encode emoji (e.g., Windows cp1252), causing devr check to crash after tests.

Description

• Add a helper _echo_with_fallback(primary, fallback) in src/devr/cli.py that calls typer.echo(primary) and falls back to ASCII-safe text when a UnicodeEncodeError is raised.
• Replace direct emoji success messages for check, fix, and security with _echo_with_fallback(...) using plain-text fallbacks.
• Add a regression test test_echo_with_fallback_uses_plaintext_when_unicode_encoding_fails in tests/test_cli.py that simulates an encoding failure and asserts the fallback is used.

Testing

• Ran the test suite with pytest -q, which passed: 92 passed in 0.79s.
• The new unit test simulating typer.echo encoding failure also passed as part of the test run.

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Codex Task