feat(navigation): add symbol index and LSP navigation features

The changes introduce a Tcl symbol index powering LSP navigation
features across the workspace. A navigation API exposes
snapshots and update hooks, enabling goto-definition,
references, and rename using the index. Background indexing
now watches Tcl files and rebuilds the index to stay in sync.

- Add Tcl symbol index and navigation snapshot API
- Wire go-to-definition, references, and rename using the index
- Watch Tcl files and refresh the index in the background

server/src/lsp_tclserver.py

@@ -15,6 +15,7 @@ from tclint.violations import Violation
 from tools import checks, parser
 from tools.completion_items import CompletionCollector
 from tools.formatter import NxFormatter as Formatter
+from tools.navigation import FileSymbolIndex, build_file_symbol_index
 from tools.proc_docs import build_proc_docs
 
 
@@ -31,6 +32,7 @@ class TclLanguageServer(server.LanguageServer):
         self.poco_completion: dict = {}
         self.proc_signatures: dict = {}
         self.proc_docs: dict = {}
+        self.navigation_indexes: dict[str, FileSymbolIndex] = {}
         # Cache: (uri, version) -> (tree, violations)
         self._ast_cache = {}
         self._parser_lock = threading.RLock()
@@ -115,6 +117,11 @@ class TclLanguageServer(server.LanguageServer):
         with self._index_lock:
             return self.diagnostics.get(uri)
 
+    def navigation_snapshot(self) -> dict[str, FileSymbolIndex]:
+        """Return an immutable snapshot of the workspace symbol indexes."""
+        with self._index_lock:
+            return dict(self.navigation_indexes)
+
     def _begin_index_update(self, filepath: str, version: int | None) -> int | None:
         with self._index_lock:
             indexed_version = self._index_versions.get(filepath)
@@ -140,6 +147,7 @@ class TclLanguageServer(server.LanguageServer):
             self.poco_completion.pop(filepath, None)
             self.proc_signatures.pop(filepath, None)
             self.proc_docs.pop(filepath, None)
+            self.navigation_indexes.pop(filepath, None)
 
     def indexed_paths_under_uri(self, uri: str) -> list[pathlib.Path]:
         target = pathlib.Path(uris.to_fs_path(uri))
@@ -147,6 +155,7 @@ class TclLanguageServer(server.LanguageServer):
             indexed_paths = set(self.poco_completion)
             indexed_paths.update(self.proc_signatures)
             indexed_paths.update(self.proc_docs)
+            indexed_paths.update(self.navigation_indexes)
             indexed_paths.update(self._index_tokens)
         return [
             pathlib.Path(path)
@@ -163,6 +172,7 @@ class TclLanguageServer(server.LanguageServer):
                 self.poco_completion,
                 self.proc_signatures,
                 self.proc_docs,
+                self.navigation_indexes,
                 self._index_tokens,
                 self._index_versions,
             ):
@@ -212,6 +222,9 @@ class TclLanguageServer(server.LanguageServer):
             )
             tree.accept(collector, recurse=True)
             docs = build_proc_docs(tree, document.source)
+            navigation_index = build_file_symbol_index(
+                filepath, document.uri, tree
+            )
         except Exception as e:
             logging.debug(f"Error parsing {filepath}: {e}")
             self._discard_index_update(filepath, token)
@@ -227,6 +240,7 @@ class TclLanguageServer(server.LanguageServer):
             self.poco_completion[filepath] = list(collector.custom_functions)
             self.proc_signatures[filepath] = dict(collector.proc_signatures)
             self.proc_docs[filepath] = docs
+            self.navigation_indexes[filepath] = navigation_index
         return True
 
     def format(