Adds packageManager during init

[arcanis]

Note

Medium Risk
Touches project initialization and package.json generation, which can affect all newly created projects; risk is moderate because changes are localized but impact default manifest fields.

Overview
yarn init now always writes a packageManager field to package.json using the running CLI version (passed through InitParams), instead of relying on INFRA_VERSION/omitting it.

When initializing a new manifest, it also seeds type: "module", and the default empty package.json template now includes a trailing newline. Separately bumps zpm-switch from 6.0.0-rc.17 to 6.0.0-rc.18 (lockfile + manifest).

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⏱️ Benchmark Results

gatsby install-full-cold

Metric	Base	Head	Difference
Mean	2.431s	2.437s	+0.26% ⚠️
Median	2.431s	2.427s	-0.18% ✅
Min	2.391s	2.383s
Max	2.467s	2.772s
Std Dev	0.019s	0.069s

📊 Raw benchmark data (gatsby install-full-cold)

Base times: 2.441s, 2.442s, 2.467s, 2.421s, 2.442s, 2.457s, 2.415s, 2.432s, 2.438s, 2.431s, 2.413s, 2.417s, 2.391s, 2.464s, 2.431s, 2.428s, 2.443s, 2.434s, 2.416s, 2.449s, 2.407s, 2.428s, 2.457s, 2.409s, 2.423s, 2.427s, 2.431s, 2.448s, 2.395s, 2.423s

Head times: 2.404s, 2.412s, 2.398s, 2.452s, 2.430s, 2.425s, 2.399s, 2.496s, 2.448s, 2.428s, 2.383s, 2.420s, 2.407s, 2.392s, 2.425s, 2.403s, 2.440s, 2.386s, 2.436s, 2.446s, 2.453s, 2.495s, 2.431s, 2.430s, 2.441s, 2.447s, 2.391s, 2.420s, 2.398s, 2.772s

---

gatsby install-cache-and-lock (warm, with lockfile)

Metric	Base	Head	Difference
Mean	0.339s	0.337s	-0.47% ✅
Median	0.339s	0.336s	-0.85% ✅
Min	0.330s	0.332s
Max	0.371s	0.348s
Std Dev	0.007s	0.004s

📊 Raw benchmark data (gatsby install-cache-and-lock (warm, with lockfile))

Base times: 0.347s, 0.339s, 0.339s, 0.347s, 0.339s, 0.338s, 0.340s, 0.340s, 0.341s, 0.337s, 0.339s, 0.337s, 0.340s, 0.341s, 0.371s, 0.339s, 0.333s, 0.339s, 0.340s, 0.334s, 0.337s, 0.331s, 0.330s, 0.336s, 0.330s, 0.338s, 0.333s, 0.335s, 0.340s, 0.331s

Head times: 0.341s, 0.337s, 0.334s, 0.338s, 0.342s, 0.345s, 0.337s, 0.336s, 0.332s, 0.341s, 0.339s, 0.348s, 0.336s, 0.341s, 0.335s, 0.333s, 0.335s, 0.336s, 0.336s, 0.337s, 0.335s, 0.335s, 0.333s, 0.335s, 0.340s, 0.332s, 0.336s, 0.336s, 0.337s, 0.336s