chore(changeset): declare the os lint --generator accept-set narrowing

`minor` with a `**BREAKING**` banner, on the `os create` project-name
precedent (#15893): while the workspace versions in lockstep the bump level
carries no breaking-ness, so the banner and the ADR-0087 disposition are the
carriers. A scripted invocation that passed `--generator` outside eval mode
exited 0 and now exits 1.

Disposition `not-required (no-migration-prescription)`: the change narrows
what a CLI flag combination accepts at invocation time, touching no metadata
surface, stored row or spec declaration.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01D47qPfEWVPmhguWgBZCi5N

Author: claude

.changeset/lint-generator-requires-eval.md

@@ -0,0 +1,13 @@
+---
+"@objectstack/cli": minor
+---
+
+**BREAKING** `os lint --generator` now refuses to run without `--eval`, instead of accepting the flag and ignoring it.
+
+The flag's own description has always ended "Requires --eval.", and nothing checked it. `--generator` is read only by eval mode, so outside `--eval` the flag reached no code at all: `os lint --generator ./gen.mjs` linted the current project, exited 0 with "All checks passed", never loaded the module, and named the flag nowhere on either the human face or `--json`. A path that did not exist was accepted just as readily. Someone who meant to score a live generator got a successful-looking run whose generator was never called, with nothing said.
+
+The refusal is this command's own, not the argument parser's, so it keeps the shape the command's other failures already have: the reason on `error`, exit 1, and on `--json` a single JSON document with stdout still reserved for the machine. No error code is invented for it.
+
+A scripted invocation that passed `--generator` outside eval mode now exits 1 with the reason, where it previously exited 0 having silently skipped the generator. Eval mode itself is untouched: `--eval --generator` still loads the module and scores live output, and `--eval` alone still scores the bundled corpus offline.
+
+<!-- adr-0087: not-required (no-migration-prescription) The change narrows what a CLI flag combination accepts at invocation time. No metadata surface, stored row or spec declaration is touched, so `objectstack migrate meta` has nothing to carry and the ledger has nothing to record. -->