fix(action-grammar): support optional rule references

[Rio Yu (rioyu123)]

Summary

• parse an adjacent ? after a named rule reference as an optional suffix
• preserve required references and literal question marks when ? is separated or escaped
• carry optionality through local, imported, and built-in phrase-set references
• keep formatter round-trips, source metadata, spacing modes, and grammar docs in sync

Why

<Owner>? was previously compiled as a required <Owner> followed by a literal ? token. That made the optional reference fail to match even though the equivalent inline group worked. The same suffix form is already used by grammars such as <TimeSpec>? and <PanelRef>?.

The suffix is intentionally adjacency-only, matching $(...)? and (...)?, so <Rule> ? remains a required reference followed by literal punctuation.

Validation

• action grammar build
• 76 action grammar test suites: 16,188 passed, 2 skipped
• parser/writer round-trip, NFA/DFA, AST evaluation, and completion regressions
• Prettier and git diff --check
• repository policy checks: 9,532 passed
• code-lint ratchet: no new violations

Fixes #2461