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_strip_html.py

@@ -0,0 +1,59 @@
+"""Tests for _strip_html edge cases."""
+
+from tuimble.app import _strip_html
+
+
+def test_plain_text_unchanged():
+    assert _strip_html("hello world") == "hello world"
+
+
+def test_simple_tags_stripped():
+    assert _strip_html("<b>bold</b>") == "bold"
+
+
+def test_nested_tags():
+    assert _strip_html("<div><p>text</p></div>") == "text"
+
+
+def test_self_closing_tags():
+    assert _strip_html("line<br/>break") == "linebreak"
+
+
+def test_entities_unescaped():
+    assert _strip_html("&amp; &lt; &gt;") == "& < >"
+
+
+def test_html_entities_in_tags():
+    assert _strip_html("<b>&amp;</b>") == "&"
+
+
+def test_mumble_style_message():
+    """Typical Mumble chat message with anchor tag."""
+    msg = '<a href="https://example.com">link text</a> and more'
+    assert _strip_html(msg) == "link text and more"
+
+
+def test_img_tag_with_attributes():
+    assert _strip_html('before<img src="x.png" alt="pic"/>after') == "beforeafter"
+
+
+def test_comment_stripped():
+    assert _strip_html("before<!-- comment -->after") == "beforeafter"
+
+
+def test_empty_string():
+    assert _strip_html("") == ""
+
+
+def test_only_tags():
+    assert _strip_html("<br><hr><img/>") == ""
+
+
+def test_unclosed_tag():
+    """Malformed HTML should not crash."""
+    result = _strip_html("<b>unclosed")
+    assert "unclosed" in result
+
+
+def test_multiple_entities():
+    assert _strip_html("&quot;quoted&quot;") == '"quoted"'