Editor grammar rejects quoted method names (`A."some method"()`) the renderer accepts

[MrCoder]

Summary

The editor's Lezer grammar rejects quoted (string) method names like A."some method"(),
which the renderer accepts. ZenUML uses quoted method names for spaced/multi-word method labels,
and this is one of the two false-positive cases explicitly blocking in-editor error feedback
(see web/src/editor/modes.ts — the Lezer linter is disabled partly because of "the shipped
quoted-method-name templates").

Steps to reproduce

Type A."some method"() (or A."do it"() { B.c() }).

Expected vs Actual

Input	Lezer (editor)	ANTLR (renderer)
A.method()	ok	ok
A."some method"()	ERROR (2 nodes)	ok
A."m"()	ERROR	ok
A.方法()	ok (Unicode, fixed by #809)	ok

Location

web/src/editor/grammar/zenuml.grammar ~line 361:

MethodName { !call Identifier }

Accepts only an Identifier; a String method name fails.

Fix sketch

MethodName { !call (Identifier | String) }

(String token already exists. Same pattern as #808's Label fix.) Regenerate the parser; verify
A."some method"() parses with 0 error nodes, conformance subset holds, and A.method() /
A.方法() still parse.

Why it matters

This is the LAST of the two named false-positive blockers in modes.ts (the other,
declare-then-message, already parses cleanly). Closing it clears the way to wiring the
already-built zenumlLinter and giving users real in-editor error feedback.

Found via the editor-improvement campaign (grammar-gap hunt toward enabling error feedback).