fix(ai): align failed browser preview policy

[first-assist]

Summary

• require the exact descriptor's browser-preview opt-in and fresh registered-tool preauthorization before returning a safe failed-call preview
• make egress-denied rows categorically non-previewable and keep protected result content behind the egress boundary
• make failure-code coverage compile-time exhaustive and verify the default argument projector continues returning None
• release the project-neutral runtime fix as graphql-orm-ai 0.93.2

Verification

• all-provider SQLite matrix: 401 unit tests observed; 398 passed, 3 ignored; every integration suite passed
• focused preview regression: 1 passed
• warning-denied clippy: passed
• warning- and missing-doc-denied rustdoc: passed
• PascalCase GraphQL naming: 1 passed; PascalCase rustdoc passed
• PostgreSQL and MSSQL compile surfaces: passed
• owned disposable PostgreSQL parity: 1 passed
• cargo-semver-checks from 0.93.1 to 0.93.2: 196 passed, 49 inapplicable, no update required
• governed documentation: 187 files passed
• generated workspace inventory, formatting, diff checks, release policy: passed
• consumer-specific term grep across the upstream diff: 0 matches

Documentation

• Documentation updated
• No documentation impact