feat(tcl): add dynamic argument completion and snippets

The changes add dynamic, semantic argument completion for Tcl
commands and snippet support.

- Introduces DynamicCompletionKind, TclArgumentCompletion, and dynamic rules
  for Tcl to provide variable, procedure, namespace, and path suggestions.
- Adds snippet-backed commands and arguments for Tcl blocks and paths.
- Refactors tcl_argument_completion and updates the LSP to use dynamic path,
  variable, and namespace completions with snippet kinds.

server/src/tools/completion_items.py

@@ -31,6 +31,7 @@ COMMAND_KINDS = {
     lsp.CompletionItemKind.Method,
     lsp.CompletionItemKind.Constructor,
     lsp.CompletionItemKind.Keyword,
+    lsp.CompletionItemKind.Snippet,
 }
 
 _VARIABLE_PREFIX_RE = re.compile(r"(?<!\\)\$(?:\{)?[A-Za-z0-9_:]*$")