CID scanning rewrites suffixes of legal host identifiers #1712

The effect scanner's ASCII word boundary treats CID inside legal host identifiers as the CID macro. On e5527d5, calling $CID(20) or πCID(20) fails compilation with Error: CID(20) names no constructor or def. JavaScript private #CID and identifiers containing a joiner have the same problem.

The patch requires a complete host identifier token, including Unicode ID_Continue, dollar, private-name and join-control boundaries. Comments and literals keep the existing scanner behavior; this is separate from #1604/#1653's line-continuation fix.

Real behavior proof: tests/io/effect_identifier_boundary.bend fails before in both C and JS builds. Afterward the actual native executable and Bun script each print 42. The JS program exercises dollar, Greek, private and joiner identifiers; the C program exercises dollar and Greek identifiers. Real CID(answer) registration still works.

Commands: bun bend2/main.ts tests/io/effect_identifier_boundary.bend -o boundary; ./boundary --threads 1 --gpu off; bun bend2/main.ts tests/io/effect_identifier_boundary.bend -o boundary.js; bun boundary.js.

Patch: oxura@7e2e021

# CID is a macro token, not a suffix of a legal host identifier.
import Base

def answer() -> IO(U32):
  import "./effect_identifier_boundary.c"
  import "./effect_identifier_boundary.js"

def main() -> IO(Unit):
  do IO<Unit>:
    value : U32 <- answer()
    IO.print(U32.show(value))

#|42

static Term $CID(Term n) { return n + 1; }
static Term πCID(Term n) { return n + 1; }

static Term answer_run(Env e, Term* f, IoWork* w) {
  (void)e;
  (void)f;
  (void)w;
  return $CID(20) + πCID(20);
}

static void __attribute__((constructor)) answer_use(void) {
  io_eff(CID(answer), answer_run);
}

function $CID(n) { return n + 1; }
function πCID(n) { return n + 1; }
function joined‍CID(n) { return n + 1; }
class Counter {
  #CID(n) { return n + 1; }
  value() { return this.#CID(10); }
}
function answer() {
  return $CID(9) + πCID(10) + joined‍CID(9) + new Counter().value();
}
io_eff(CID(answer), answer);