test: add _strip_html edge cases and config validation tests

strip_html: nested tags, malformed HTML, comments, entities.
config: unknown key filtering, missing file, mixed valid/invalid.

tests/test_config.py

@@ -1,6 +1,9 @@
 """Tests for configuration module."""
 
-from tuimble.config import AudioConfig, Config, PttConfig, ServerConfig
+from tuimble.config import (
+    AudioConfig, Config, PttConfig, ServerConfig,
+    _load_section, load_config,
+)
 
 
 def test_default_config():
@@ -45,3 +48,47 @@ def test_server_cert_custom():
     srv = ServerConfig(certfile="/path/cert.pem", keyfile="/path/key.pem")
     assert srv.certfile == "/path/cert.pem"
     assert srv.keyfile == "/path/key.pem"
+
+
+# -- _load_section tests -----------------------------------------------------
+
+
+def test_load_section_filters_unknown_keys():
+    """Unknown keys are silently dropped, valid keys are kept."""
+    result = _load_section(ServerConfig, {
+        "host": "example.com",
+        "typo_field": "oops",
+        "another_bad": 42,
+    })
+    assert result.host == "example.com"
+    assert result.port == 64738  # default preserved
+
+
+def test_load_section_empty_dict():
+    result = _load_section(PttConfig, {})
+    assert result.key == "f4"
+    assert result.mode == "toggle"
+
+
+def test_load_section_all_valid():
+    result = _load_section(PttConfig, {"key": "space", "mode": "hold"})
+    assert result.key == "space"
+    assert result.mode == "hold"
+
+
+def test_load_config_missing_file(tmp_path):
+    """Missing config file returns defaults."""
+    cfg = load_config(tmp_path / "nonexistent.toml")
+    assert cfg.server.host == "localhost"
+
+
+def test_load_config_with_unknown_keys(tmp_path):
+    """Config file with unknown keys loads without error."""
+    toml = tmp_path / "config.toml"
+    toml.write_text(
+        '[server]\nhost = "example.com"\nbogus = true\n'
+        '[ptt]\nfuture_option = "x"\n'
+    )
+    cfg = load_config(toml)
+    assert cfg.server.host == "example.com"
+    assert cfg.ptt.key == "f4"  # default, not overwritten