Add profile card contract example

[alexgduarte]

Contributes to #11

Summary

• Add a new profile-card simple contract example.
• Let addresses create, update, clear, and remove profile records.
• Add owner controls, validation, single-profile queries, paginated profile listing, README documentation, schema generation, and root README linking.
• Include five focused unit tests.

Validation

• cargo fmt --manifest-path profile-card/Cargo.toml -- --check
• cargo test --manifest-path profile-card/Cargo.toml --target-dir /private/tmp/codex-profile-card-target
• git diff --check