`exit program` (as documented in the keyword reference) does not parse; bare `exit` is a silent no-op at top level

[logbie]

Summary

exit program — the form given in the keyword reference — does not parse. Bare exit parses but is a no-op at top level: the program keeps running and exits 0. Neither spelling produces the documented "exit program" behaviour.

Reproduction

Documented form:

display "before"
exit program
display "after"

Bare form:

display "before"
exit
display "after"

Command:

wfl d2_exit_program.wfl
wfl d2_exit_bare_noop.wfl

Expected

Both should print before and stop. Docs/reference/reserved-keywords.md:610
lists exit under Control Flow with the usage column reading exit program,
and Docs/reference/keyword-reference.md:32 describes it as
| exit | Exit program/loop | ✗ |.

Actual

exit program:

error[ANALYZE-SEMANTIC]: Variable 'program' is not defined

Exit code: 3. (program is parsed as an operand, not part of the statement.)

Bare exit:

before
after

Exit code: 0 — the statement is accepted and does nothing.

Inside a loop, bare exit behaves like break (leaves the innermost loop and
continues afterwards); that part is coherent, but it is the loop half of the
documented "Exit program/loop" and the program half has no working spelling.

The statement exists in the AST and is executed as a control-flow signal:

// src/parser/ast.rs:232
ExitStatement { line: usize, column: usize },

// src/interpreter/mod.rs:7842-7846
Statement::ExitStatement { .. } => {
    Ok((Value::Null, ControlFlow::Exit))
}

ControlFlow::Exit is honoured by the loop drivers but not at program top level,
so the documented program-termination behaviour is unreachable.

Environment

• wfl --version: WebFirst Language (WFL) version 26.8.4
• binary: system install C:\Program Files\wfl\bin\wfl.exe
• commit: c277d8f
• OS: Windows 11 Pro 10.0.26200
• build: release

Also reproduces on the repo build (26.8.2) — not a regression.
No .wflcfg in scope.

Context

Found while porting G:/repos/JShrink/src/JShrink/Minifier.php (a 738-line PHP
JavaScript minifier) to WFL. The port's CLI needs an early exit on a missing
argument, which is what sent us to exit.

This was encountered, not blocking — the port instead prints a usage line and
forces a nonzero status (see the companion issue on raising a fatal error with a
custom message). No stub was left.

Either half is a valid fix and they are independent: make exit program parse and
terminate with status 0, or make bare exit terminate at top level — but the two
reference pages should agree with whichever ships, since today they document a form
that errors and a form that silently does nothing.