[verified] fix: register missing TypeScript and C# context docs for issue #322

[zhao0112]

Summary

• Registers three missing built-in context entries in registry.json: TypeScript, C# language, and C# Project Structure.
• Fixes registry dependency validation to recognize skill: targets by mapping them to skills.
• Adds a guarded dependency lookup in scripts/registry/validate-registry.sh to avoid set -e exits when dependency resolution fails in command substitution.

Checks

• python3 -m json.tool registry.json
• bash -n scripts/registry/validate-registry.sh
• ./scripts/registry/validate-registry.sh --verbose
• npm run -s validate:registry:verbose

Verification

• Independent reviewer prompt (delegate_task) passed with no security or logic blockers.

Closes #322