Integrate "start with an example" flow into the CLI

[yamcodes]

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[yamcodes]

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Agent Brief

Category: enhancement
Summary: Add an interactive "Select Example" step to the arkenv init wizard

Current behavior:
The CLI sets up a blank configuration. Users must manually look at the repo or docs to find examples.

Desired behavior:
During init, the CLI should offer a list of common templates (e.g., "Vite + Zod", "Next.js + ArkType") and scaffold the environment files based on the selection.

Key interfaces:

• Template Registry — a way for the CLI to fetch or reference example configurations.
• Scaffold logic — needs to support copying from templates.

Acceptance criteria:

• A new prompt in arkenv init asks: "Would you like to start with an example?".
• Selecting an example populates the env.ts and .env files with template content.
• At least 3 standard examples are available.

Out of scope:

• Downloading templates from the internet (should use internal templates for now).