fix(cli): persist auto-scale rules in JSON mode

[mhb888248]

What

• keep JSON mode as an output-format choice instead of an implicit dry-run
• persist auto-scale rules before emitting JSON when --dry-run is absent
• preserve non-mutating behavior for --json --dry-run
• add an integration regression test that verifies the config file is written

Why

sh1pt scale auto --json returned the requested rules and exited before saveAutoScaleRules(). Automation saw a successful JSON response even though no configuration file existed, so the requested auto-scale policy was silently discarded.

Reproduction

Before this change, the command printed valid JSON but .sh1pt/auto-scale.json did not exist. After the change, the same command writes the file; adding --dry-run still skips the write.

Testing

• pnpm exec vitest run packages/cli/src/commands/scale.test.ts (55 passed)
• isolated CLI reproduction before/after using a temporary home directory
• pnpm --filter @profullstack/sh1pt... build
• pnpm --filter @profullstack/sh1pt typecheck

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[github-actions]

🤖 Auto-rebase: The branch was rebased successfully locally but could not be pushed to the fork. Please enable 'Allow edits from maintainers' in the PR settings, or rebase manually: git fetch upstream master && git rebase upstream/master.