fix(angular): fix 3 control flow parity gaps with Angular reference

[Brooooooklyn]

• Fix empty parentheses in on-triggers (e.g. idle(), hover()) being
  incorrectly treated as having parameters. Angular's consumeParameters()
  returns zero parameters for empty parens.
• Add viewport trigger parameter arity validation using top-level comma
  splitting to reject viewport(a,b) while accepting object literals
  like viewport({trigger: foo, rootMargin: "123px"}).
• Fix @defer (on ) and @defer (when ) falling through to
  "Unrecognized trigger" error after lexer trimming. Now recognizes bare
  "on"/"when" keywords and matches Angular's silent acceptance.

Co-Authored-By: Claude Opus 4.6 noreply@anthropic.com

---

Note

Medium Risk
Changes affect control-flow parsing and error reporting for @defer triggers, so mismatches could alter accepted syntax or emitted diagnostics, but the scope is narrow and covered by new tests.

Overview
Improves @defer trigger parsing parity with Angular by treating empty parentheses like idle()/viewport() as no parameters, recognizing bare on/when keywords after trimming and silently accepting @defer (on ) / @defer (when ) instead of erroring.

Adds pre-parse arity validation for the viewport trigger using top-level comma splitting so viewport(a,b) errors while object-literal options containing nested commas are still accepted, and extends r3_template_transform_test.rs with focused regression coverage for these cases (plus a few error-recovery/cascade expectations).

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[Brooooooklyn]

• fix(angular): fix 3 control flow parity gaps with Angular reference #32 👈 (View in Graphite)
• main

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