Add tiered .asc parser with companion netlist resolution

Implement three-tier resolution for LTspice .asc schematic files:

1. Companion netlist - finds .net/.cir/.sp beside the .asc (automatic)
2. LTspice generation - invokes LTspice binary (opt-in via --generate-netlist)
3. Metadata-only fallback - extracts component refs/values without connectivity

Safety: DataCompleteness enum forces callers to check completeness.
CLI blocks diagram generation on METADATA_ONLY with clear remediation.
Metadata enrichment is additive-only with protected field guards.

Also: update project URLs to Gitea, add .asc usage docs to README,
fix pre-existing ruff warning in test_single_module.py.

tests/test_cli.py

@@ -128,3 +128,75 @@ class TestCLIFiltering:
         )
         assert result.exit_code == 0
         assert "X1:" not in result.output
+
+
+class TestCLIAscInput:
+    """Tests for .asc file input through the CLI."""
+
+    def test_asc_with_companion_works(self):
+        """simple_board.asc has companion .net — full pipeline should work."""
+        runner = CliRunner()
+        result = runner.invoke(
+            main,
+            [str(FIXTURES / "simple_board.asc"), "-s", "amplifier_board"],
+        )
+        assert result.exit_code == 0
+        assert "connectors:" in result.output
+        assert "amplifier_board" in result.output
+
+    def test_asc_companion_resolution_in_stderr(self):
+        """CLI should report which .net was resolved to stderr."""
+        runner = CliRunner()
+        result = runner.invoke(
+            main,
+            [str(FIXTURES / "simple_board.asc"), "-s", "amplifier_board"],
+        )
+        assert result.exit_code == 0
+        assert "simple_board.net" in result.stderr
+
+    def test_asc_without_companion_errors(self):
+        """standalone.asc has no companion .net — diagram generation should fail."""
+        runner = CliRunner()
+        result = runner.invoke(main, [str(FIXTURES / "standalone.asc")])
+        assert result.exit_code != 0
+        assert "connectivity" in result.output.lower() or "connectivity" in (
+            getattr(result, "stderr", "") or ""
+        ).lower()
+
+    def test_asc_without_companion_shows_remediation(self):
+        """Error message should tell the user how to fix it."""
+        runner = CliRunner()
+        result = runner.invoke(main, [str(FIXTURES / "standalone.asc")])
+        assert result.exit_code != 0
+        stderr = result.stderr
+        assert "--generate-netlist" in stderr or "--list-components" in stderr
+
+    def test_asc_list_components_on_metadata_only(self):
+        """--list-components should work even without connectivity."""
+        runner = CliRunner()
+        result = runner.invoke(
+            main,
+            [str(FIXTURES / "standalone.asc"), "--list-components"],
+        )
+        # Should succeed (exit 0) — inspection doesn't need connectivity
+        assert result.exit_code == 0
+
+    def test_asc_list_subcircuits_with_companion(self):
+        """--list-subcircuits through .asc with companion works."""
+        runner = CliRunner()
+        result = runner.invoke(
+            main,
+            [str(FIXTURES / "simple_board.asc"), "--list-subcircuits"],
+        )
+        assert result.exit_code == 0
+        assert "amplifier_board" in result.output
+
+    def test_asc_dry_run_with_companion(self):
+        """--dry-run through .asc with companion produces summary."""
+        runner = CliRunner()
+        result = runner.invoke(
+            main,
+            [str(FIXTURES / "simple_board.asc"), "-s", "amplifier_board", "--dry-run"],
+        )
+        assert result.exit_code == 0
+        assert "Mode: single" in result.output