feat(lab2): Threagile threat model + secure variant + auth flow

[ratteperk]

Goal

• Generate a STRIDE-based threat model of OWASP Juice Shop with Threagile, then produce a secure-variant model and diff the risk reports.

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Changes

• submissions/lab2.md - risk analysis tables and STRIDE mapping
• labs/lab2/threagile-model-secure.yaml - hardened model with HTTPS and encryption
• labs/lab2/threagile-model-auth.yaml - smaller Threagile model focused on Juice Shop's authentication flow

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Testing

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Artifacts & Screenshots

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• Task 1 — Baseline risk table + top-5 with STRIDE mapping
• Task 2 — Secure variant + risk diff table
• Bonus — Auth-flow model + 3 auth-specific risks