Extend TemplateCompileTests + lockfiles to V0/V2 templates

[stevenfackley]

V1-DotNet-NextJs is the only template with a package-lock.json (#294) and the only one gated by Engine V1TemplateCompileTests (render -> docker build) — that gate caught the 2026-08-19 lock desync (fixed in #312). V0-Spark and the V2 templates have neither, so their dependency bumps are semver-trust only. Add lockfiles + compile tests so every template bump gets the same gate.

[stevenfackley]

V0 half landed in #315: the Spark template now has a real compile gate (render through the production path → npm install → next build, toolchain-guarded so it hard-fails on CI if npm goes missing). Deliberately no lockfile for V0 — StackBlitz WebContainers installs fresh from the exact pins, and a lock would ride inside preview_files_json on every free generation row; with no lock, the manifest/lock desync class can't exist there.

Remaining scope for this issue: V2-DotNet-NextJs (dev-only, prod-off — gate + lockfile when the Swiss-Cheese path matters again) and the V1/V2-Python-React frontends (no gate at all today). The Tier3 CDK dir is already gated by Tier3InfrastructureCompileTests — that gate is what caught TS7 breaking ts-node on #267.