fix(case-init): reject unknown presets before writing

[Yu-0312]

Summary

• Reject unknown --preset values in the Bash and PowerShell case initializers before any case artifacts are written.
• Add Bash and Windows PowerShell regression coverage for fail-fast behavior and partial-case prevention.
• Document the behavior change in CHANGELOG.md.

Problem

A typo in a non-empty preset previously emitted a warning but exited successfully. The initializer then continued with pending/offline defaults and created a case directory, making it easy to mistake a requested preset for an applied preset.

Solution

Unknown presets now return a non-zero exit before the case directory is created. Existing aliases remain unchanged: offline-sample, own-sample, local-sample, ctf-public, ctf, own-system, and lab-only.

Tests

• bash skills/scripts/test-routing.sh — 173/173 passed
• bash skills/scripts/test-bootstrap-manifest.sh — passed
• bash skills/scripts/test-bash-workflow.sh — passed
• python3 skills/case-review/tests/test_review_case.py — 8/8 passed
• JSON validation and git diff --check — passed