chore: add coverage configuration to pyproject.toml

Configure pytest-cov with:
- Branch coverage enabled for stackone_ai source
- Exclusions for __init__.py and py.typed files
- Standard exclusion patterns (TYPE_CHECKING, NotImplementedError, etc.)
- JSON output to coverage/coverage.json for CI badge generation
- HTML output to coverage/html for detailed reports

Author: ryoppippi

pyproject.toml

@@ -123,3 +123,26 @@ ignore_missing_imports = true
 module = "mcp.*"
 ignore_missing_imports = true
 ignore_errors = true
+
+[tool.coverage.run]
+source = ["stackone_ai"]
+branch = true
+omit = [
+    "stackone_ai/__init__.py",
+    "**/py.typed",
+]
+
+[tool.coverage.report]
+exclude_lines = [
+    "pragma: no cover",
+    "def __repr__",
+    "raise NotImplementedError",
+    "if TYPE_CHECKING:",
+    "if typing.TYPE_CHECKING:",
+]
+
+[tool.coverage.json]
+output = "coverage/coverage.json"
+
+[tool.coverage.html]
+directory = "coverage/html"