docs(jobs): a job body's default locale and time zone are the server's (#29355)

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Fixes #29202
Clause-②: no
Metadata-protocol: none

## 维护者速读
- 改了什么：定时任务文档 `jobs.mdx` 在 `Intl.DateTimeFormat` 那条说明里补两句话：不传语言和
`timeZone` 时用的是服务器的默认语言和时区，要稳定输出就显式传 `timeZone`（和语言）。
- 为什么改：开发者本地跑和服务器跑会得到不同的日期，文档之前没提醒；这是 #29031 合约复审点名的后续。
- 风险与回滚：纯文档，不改代码、不发布任何包；回滚即还原这 5 行。
- 先看：`content/docs/automation/jobs.mdx` 第 199–203 行（新增的两句与示例）。
- 两分钟验证：打开文档站「Jobs」页的沙箱一节，`Intl.DateTimeFormat` 那条下应看到 “server's default
locale and time zone” 与 `{ timeZone: 'UTC' }` 示例。
- 需要你做的：无，席位落地。

## What changes

One addition to the `Intl.DateTimeFormat` bullet in
`content/docs/automation/jobs.mdx` (+5 / -0): a formatter built with no
locale or `timeZone` uses the server's default locale and time zone, and
its `resolvedOptions()` reports them; a body should pass `timeZone` (and
a locale) for output that does not depend on where it runs, with `new
Intl.DateTimeFormat('en-US', { timeZone: 'UTC' })` as the example. No
code change.

## Tests

None owed: docs only, no tested behaviour changes. The statement was
measured before it was written (below).

## Acceptance notes

- The wiring that backs the sentence: the VM-side constructor in
`packages/runtime/src/sandbox/sandbox-intl.ts` snapshots `locales` /
`options`; with neither given the snapshot is empty, `readSnapshot`
hands `undefined` / `undefined` to the host, and `installSandboxIntl`
builds `new Intl.DateTimeFormat(locales, options)` with the host's own
`Intl`, so the host's defaults apply. `QuickJSScriptRunner.execute()` in
`packages/runtime/src/sandbox/quickjs-runner.ts` calls
`installSandboxIntl(vm)` for every body kind.
- Hook and action pages (`content/docs/automation/hooks.mdx`,
`content/docs/automation/hook-bodies.mdx`,
`content/docs/ui/actions.mdx`) do not carry the `Intl.DateTimeFormat`
bullet, so there is nothing to mirror there; the jobs bullet already
says hook and action bodies get the same formatter.
- No changeset: `content/docs` ships in no package's `files[]`, so
`skip-changeset`.

## Verification

<details><summary>Measured: a no-option formatter answers the host's
locale and zone</summary>

A scratch script installed `installSandboxIntl` into a fresh QuickJS
context (the same call `execute()` makes) and evaluated `new
Intl.DateTimeFormat().resolvedOptions()` and `.format(0)` inside the VM,
beside a formatter given `'en-US', { timeZone: 'UTC' }`, under three
host settings:

| Host `TZ` / locale | No-option `resolvedOptions()` | No-option
`format(0)` | Pinned `format(0)` |
|:--|:--|:--|:--|
| `Asia/Tokyo` / `de_DE` | `de-DE`, `Asia/Tokyo` | `1.1.1970` |
`1/1/1970` |
| `America/New_York` / `de_DE` | `de-DE`, `America/New_York` |
`31.12.1969` | `1/1/1970` |
| `Asia/Tokyo` / `en_GB` | `en-GB`, `Asia/Tokyo` | `01/01/1970` |
`1/1/1970` |

Each no-option row equals the host's own `new
Intl.DateTimeFormat().resolvedOptions()` in the same process; the pinned
formatter answers the same in all three. The script was not committed.
</details>

<details><summary>Derived gates at 7dc9c8c (after merging origin/main
a2fcede)</summary>

`node scripts/pm/dispatch-gates.mjs --commands --repo
objectstack-ai/objectstack`: 43 commands. All 43 ran, each exit code
captured before any pipe: 43 at exit 0. Four first refused with exit 3
(PREREQUISITE NOT MET: `@objectstack/lint` / `@objectstack/formula` /
`@objectstack/client-react` not built); after `pnpm --filter
'@objectstack/lint...' --filter '@objectstack/client-react...' build`
(VERDICT command-exit 0) each re-ran at exit 0:
`check:doc-formula-expressions`, `check:doc-security-posture`,
`check:skill-examples`, `check:docs-transcript-drift`.

`--ran` reconciliation: 43 derived, 43 run, 0 NOT-MEASURED, 0 UNRUN (a
derived zero: all 43 recorded an exit code).

NOT MEASURED locally, left to CI: `ci.yml · Build Docs` and `ci.yml ·
Plan Test Core shards`, and the type-check lanes the derivation lists.
</details>

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

Author: objectstack-fleet[bot]

content/docs/automation/jobs.mdx

@@ -196,6 +196,11 @@ What running in the sandbox means for the code in `source`:
   `resolvedOptions`), and answers exactly as the server's own does, so a body can
   find the calendar date or period of an instant in a named IANA zone:
   `new Intl.DateTimeFormat('en-CA', { timeZone: 'Asia/Shanghai', year: 'numeric', month: '2-digit', day: '2-digit' }).format(Date.now())`.
+  With no locale or `timeZone`, a formatter uses the server's default locale and
+  time zone (its `resolvedOptions()` reports them), so the same body can print a
+  different date on your machine than on the server. Pass `timeZone`, and a
+  locale, for output that does not depend on where the body runs:
+  `new Intl.DateTimeFormat('en-US', { timeZone: 'UTC' })`.
   Nothing else of `Intl` is there (`Intl.NumberFormat` is `undefined`); test for
   it with `typeof Intl.DateTimeFormat === 'function'`. Hook and action bodies run
   in the same sandbox and get the same `Intl.DateTimeFormat`.