authzprobe init: scaffold identities.yaml from a spec

[PRAteek-singHWY]

Add an authzprobe init command that reads a spec, enumerates every path param and security scheme, and writes a well-commented starter identities.yaml for the user to fill in.

Files: new src/cli.ts subcommand, helpers in src/spec/parse.ts

Acceptance criteria

• Generates a valid, commented config skeleton.
• Covered by a test using the example spec.

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