feat(server): add TCL signature help support

Adds a signature help system for TCL commands.
The LSP server now exposes signature help for custom and
built-in MOM procedures, enabling parameter hints while editing.
Tests and documentation were added to cover common usage.

- Adds signature_help module to parse and present signatures
- Integrates with LSP server to provide signature help on the client
- Adds tests for custom and built-in procedures

server/tests/python_tests/test_signature_help.py

@@ -0,0 +1,92 @@
+import sys
+from pathlib import Path
+
+
+THIS_DIR = Path(__file__).parent
+SRC_DIR = THIS_DIR.parent.parent / "src"
+if str(SRC_DIR) not in sys.path:
+    sys.path.insert(0, str(SRC_DIR))
+
+import lsprotocol.types as lsp  # type: ignore
+
+from common.load_data import standard_items
+from tools.parser import CustomParser
+from tools.signature_help import build_signature_help, find_active_call
+
+
+CUSTOM_SIGNATURES = {
+    "SERVICE_spacer_output": ["type", "length", "line_num", "output"]
+}
+
+
+def test_custom_proc_signature_and_active_parameter():
+    source = 'SERVICE_spacer_output "*" '
+    tree = CustomParser().parse(source)
+
+    result = build_signature_help(
+        source,
+        tree,
+        lsp.Position(line=0, character=len(source)),
+        CUSTOM_SIGNATURES,
+        {"SERVICE_spacer_output": "Outputs a spacer line."},
+        [],
+    )
+
+    assert result is not None
+    assert result.active_parameter == 1
+    signature = result.signatures[0]
+    assert signature.label == "SERVICE_spacer_output type length line_num output"
+    assert (  # type: ignore[union-attr]
+        signature.documentation.value == "Outputs a spacer line."
+    )
+    assert signature.parameters is not None
+    assert signature.parameters[3].label == (43, 49)
+
+
+def test_innermost_command_is_used_for_nested_call():
+    source = 'set result [SERVICE_spacer_output "*" 20]'
+    tree = CustomParser().parse(source)
+    position = lsp.Position(line=0, character=source.index("20"))
+
+    call = find_active_call(source, tree, position)
+
+    assert call is not None
+    assert call.name == "SERVICE_spacer_output"
+    assert call.active_argument == 1
+
+
+def test_builtin_signature_includes_parameter_documentation():
+    source = "MOM_abort "
+    tree = CustomParser().parse(source)
+
+    result = build_signature_help(
+        source,
+        tree,
+        lsp.Position(line=0, character=len(source)),
+        {},
+        {},
+        standard_items.json_data["MOM_procs"],
+    )
+
+    assert result is not None
+    assert result.active_parameter == 0
+    signature = result.signatures[0]
+    assert signature.label == "MOM_abort <message>"
+    assert signature.parameters is not None
+    assert signature.parameters[0].documentation
+
+
+def test_unknown_command_has_no_signature_help():
+    source = "unknown_custom_command "
+    tree = CustomParser().parse(source)
+
+    result = build_signature_help(
+        source,
+        tree,
+        lsp.Position(line=0, character=len(source)),
+        {},
+        {},
+        standard_items.json_data["MOM_procs"],
+    )
+
+    assert result is None