Add a 'metadata removed' event when admin clears stored metadata

[greatest0fallt1me]

Description

This is a smart-contract issue for the GrantFox campaign. Emit a structured MetadataRemoved(subject, key) event when admin clears subject metadata.

Requirements and Context

• Event topic pattern matches index
• Tested
• Emitted from remove_metadata path
• Documented
• Must be secure, tested, and documented
• Should be efficient and easy to review

Suggested Execution

1. Fork the repo and create a branch

   git checkout -b task/metadata-removed-event

2. Implement changes
   • contracts/settlement/src/lib.rs
   • contracts/settlement/src/events.rs
   • docs/EVENT_SCHEMA.md
3. Test and commit
   • Run the repo's standard test suite and lint
   • Cover edge cases; include output in the PR

Example commit message

feat: emit MetadataRemoved event

Acceptance Criteria

• Topic correct
• Test asserts
• Doc updated
• No regressions

Guidelines

• Minimum 95% test coverage with cargo test
• require_auth on every state-changing entrypoint
• Overflow-safe math; no unwrap() in production paths
• Clear NatSpec-style /// rustdoc
• Timeframe: 96 hours

[Vibeofkd]

Hi I’d love to work on this issue

[emynogithub]

@emynogithub has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I have the skill it takes to work on this issue , please give me the opportunity to show my competence in problems solving

ℹ️ Repo Maintainers: To accept this application, review their application or assign @emynogithub to this issue.

[drips-wave]

Congratulations, @emynogithub! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @emynogithub: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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