feat(server): index PSC scripts and provide cross-file TclOO navigation/completions

Add PSC (.psc) indexing and share TclOO class metadata across files so class
definitions discovered via PSC layers can be used for completions, signature
help, inlay hints, and "go to definition". Key behavior changes:

- Client file watcher now includes *.psc and .vscode launch paths/tests updated
  to use the postprocessor test folder; .gitignore updated to ignore that folder.
- Server watches .psc changes and refreshes a PSC script index; new
  tools/tcloo_navigation.py exposes tcloo_definition used by the language server
  to resolve cross-file class/constructor/method definitions.
- Language server uses class_snapshot(document.path) when producing TclOO
  completions, signature help, and inlay hints so resolved class metadata is
  available across files.

Also includes related docs/changelog updates, minor code formatting cleanups,
and added tests for PSC/TclOO behavior.

server/src/tools/tcloo_arguments.py

@@ -38,14 +38,14 @@ def method_parameters(parameters: str) -> list[MethodParameter]:
         return []
 
 
-def method_signature_help(source: str, position: lsp.Position) -> lsp.SignatureHelp | None:
+def method_signature_help(source: str, position: lsp.Position, external_classes=None) -> lsp.SignatureHelp | None:
     lines = source.split("\n")
     if position.line >= len(lines):
         return None
     # AST columns are codepoints; LSP columns are UTF-16 code units.
     prefix = lines[position.line].encode("utf-16-le")[:position.character * 2].decode("utf-16-le", errors="ignore")
     cursor = (position.line, len(prefix))
-    candidates = [call for call in resolved_method_calls(source)
+    candidates = [call for call in resolved_method_calls(source, external_classes)
                   if _contains_cursor(call.command, lines, cursor)]
     if not candidates:
         return None