docs: document operator-facing scripts (cutover-dry-run, cutover-mailout, reconcile, setup-dev-data)

## Gap

Four \`apps/api/scripts/*\` operator-facing scripts exist with no doc entry in \`docs/operations/\` or the relevant spec:

| Script | What it does | Where it should be documented |
|---|---|---|
| \`cutover-dry-run.ts\` | Walks the full cutover pipeline against a non-prod target — used during T-3 staging rehearsal | \`docs/operations/cutover.md\` (T-3 section) |
| \`cutover-mailout.ts\` | Sends T+90 unclaimed-account reminder emails | \`docs/operations/cutover.md\` (T+90 section) or \`specs/behaviors/account-migration.md\` |
| \`reconcile.ts\` | Walks Person records and flags private-store orphans (used at cutover + ongoing) | \`docs/operations/runbook.md\` (maintenance) — referenced once in \`specs/behaviors/private-storage.md:99\` but no operator instructions |
| \`setup-dev-data.ts\` | Seeds gitsheets with minimal sheet configs for local boot | \`specs/architecture.md\` Build/dev section + \`CLAUDE.md\` local setup |

## Why it matters

Pre-cutover, the staging rehearsal (#54) needs operators to know these exist + how to invoke them. Local-setup contributors hit \`setup-dev-data.ts\` on first run and may not know what they're running.

Identified during the 2026-05-30 post-cutover-blog spec-drift audit.

首先阅读 apps/api/scripts/cutover-dry-run.ts、cutover-mailout.ts、reconcile.ts 和 setup-dev-data.ts，然后将它们与 docs/operations/cutover.md、docs/operations/runbook.md、specs/behaviors/account-migration.md、specs/behaviors/private-storage.md、specs/architecture.md 和 CLAUDE.md 进行对照。在 issue 指定的位置记录每个脚本的用途、调用方式和运维上下文，包括现有的 private-storage 引用。完成的标准是，运维人员能够找到并理解用于 cutover、维护和本地设置的全部四个脚本。

由索引模型根据 Issue 内容生成。