chore: enable import-untyped and import-not-found mypy checks

Remove global ignore_missing_imports and the import-untyped disable,
replacing them with targeted per-package overrides for third-party
libraries that lack stubs (pcbnew, skip, sexpdata, cairosvg, kipy,
schematic). Also add python/ to mypy_path so internal modules resolve.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pyproject.toml

@@ -15,13 +15,11 @@ line_length = 100
 python_version = "3.10"
 warn_return_any = false
 warn_unused_configs = true
-ignore_missing_imports = true
 check_untyped_defs = false
 disallow_untyped_defs = false
 explicit_package_bases = true
-mypy_path = "."
+mypy_path = ".:python"
 disable_error_code = [
-    "import-untyped",
     "arg-type",
     "attr-defined",
     "union-attr",
@@ -37,3 +35,20 @@ disable_error_code = [
     "return-value",
     "operator",
 ]
+
+[[tool.mypy.overrides]]
+module = [
+    "pcbnew",
+    "pcbnew.*",
+    "skip",
+    "skip.*",
+    "sexpdata",
+    "sexpdata.*",
+    "cairosvg",
+    "cairosvg.*",
+    "kipy",
+    "kipy.*",
+    "schematic",
+    "schematic.*",
+]
+ignore_missing_imports = true