feat(tcl): add static variable name extraction and array key completion

This adds tooling to statically extract Tcl variable names from syntax
trees without evaluating substitutions, enabling better completions
for array elements and plain variables. The new helpers are wired
into the completion and navigation flows and are supported by tests
covering array keys and substitutions.

- Introduce variable_names.py with variable_name() and array_key_parts()
- Wire static name extraction into completion and symbol indexing
- Add tests for array key completion with substitutions

server/src/tools/navigation.py

@@ -4,7 +4,8 @@ from dataclasses import dataclass
 from pathlib import Path
 
 import lsprotocol.types as lsp
-from tclint.syntax_tree import Command, List, Node, Script, VarSub
+from tclint.syntax_tree import Command, List, Node, QuotedWord, Script, VarSub
+from tools.variable_names import array_key_parts, variable_name
 
 ROOT_NAMESPACE = "::"
 
@@ -27,6 +28,9 @@ class SymbolOccurrence:
     fallback_identity: SymbolIdentity | None = None
     caller: SymbolIdentity | None = None
     declaration_range: lsp.Range | None = None
+    array_element: str | None = None
+    array_parts: tuple[str | None, ...] = ()
+    array_template_parts: tuple[str | None, ...] = ()
 
 
 @dataclass(frozen=True)
@@ -96,6 +100,8 @@ def _name_range(node: Node, raw_name: str, *, variable_sub: bool = False) -> lsp
         column += 2 if getattr(node, "braced", False) else 1
     else:
         position = getattr(node, "contents_pos", None) or node.pos
+        if isinstance(node, QuotedWord) and node.contents is None and node.children:
+            position = node.children[0].pos
         line, column = position
 
     normalized = _without_array_index(raw_name)
@@ -312,6 +318,13 @@ def build_file_symbol_index(
                 is_definition=is_definition,
                 symbol_kind=lsp.SymbolKind.Variable,
                 container_name=_container_name(symbol_identity),
+                array_element=(
+                    raw_name.split("(", 1)[1][:-1]
+                    if "(" in raw_name and raw_name.endswith(")")
+                    else None
+                ),
+                array_parts=array_key_parts(node),
+                array_template_parts=array_key_parts(node, preserve_variables=True),
             )
         )
 
@@ -444,7 +457,7 @@ def build_file_symbol_index(
         for node, is_definition in _variable_command_nodes(command):
             if id(node) in declaration_ids:
                 continue
-            raw_name = _static_contents(node)
+            raw_name = variable_name(node)
             if raw_name:
                 add_variable(
                     node,