docs: cut the release log out of AGENTS.md, and correct what went stale

`AGENTS.md` (which CLAUDE.md symlinks) was 158KB, and `## Status` alone was
104KB of it — 65% of a file that loads into every session's context, spent on a
per-release narrative for every cut back to 0.20.15. `CHANGELOG.md` is the log.
Status now carries the current state: where the versions are, what the npm
lockstep set is, and the publish-what-changed rule that makes a lagging number
information rather than drift. 158KB → 64KB, with every durable rule, doctrine
and cross-port contract kept intact.

Four statements had gone stale, each one a reader would act on:

  - **URL prefix policy** still said `apiPrefix` "flows through codegen to both
    route registration and hook fetch URLs". 1.0 moved the browser's base URL
    to the runtime provider — it is a deployment fact, not a build-time one.
    The section now draws that line and names the `baseUrl` trap.
  - **`@metaobjectsdev/codegen-ts/generators`** was described as a deprecated
    but working import path for the four ownable generators. It was REMOVED at
    the 1.0 cut.
  - **`field.enum` int-backed storage** was listed as deferred. `@intValueMap`
    shipped in 0.23.2, in all five ports, with two load-error rulings.
  - **The filter operators were counted three different ways** in one file —
    "Eight operators" over a list of nine, and "10 filter operators" in Status.
    `FILTER_OPS` has nine.

Also: `Useful commands` listed `init`/`gen`/`migrate` only, so a reader looking
for `verify`, `docs`, `eject`, `upgrade`, `types` or `migrate apply-pending`
found none of them — every entry checked against the CLI's own help. And
`Open questions` held three bullets of which two were answers; the closed ones
move to a "recorded so they are not re-proposed" note, which is what they were
actually doing there.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NTcEKXTQMYt84fAjuw5A2M

Author: dmealing