feat(mysql): preview Community routine invocations

[openai0229]

Summary

• add native mysql_async parameter metadata and Community-compatible FUNCTION/PROCEDURE invocation SQL previews
• expose POST /api/rdb/routine/preview_invocation through the shared Axum HTTP and desktop legacy_request path
• preserve zero-parameter and unknown-routine behavior, quoted identifiers, parameter modes/defaults, and Java dormancy

Validation

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets --all-features --locked -- -D warnings
• Contract/Core/Web focused library tests: 262 passed, 1 ignored
• native MySQL 8.4 integration: Core product, Console, and Web/desktop product tests passed
• make verify
• git diff --check

Packaging

• Original Community frontend and styles are unchanged.
• No local package was produced.
• The macOS Package workflow was not dispatched.

Closes #12