feat(mysql): complete native metadata parity slice

[openai0229]

Summary

• add native mysql_async columns, indexes, primary/imported/exported keys, views, functions, procedures, parameters, and triggers
• map 16 historical Community metadata routes through Axum HTTP and desktop dispatch without changing the original frontend
• preserve Community paging, name/comment search, complete-list filtering, counted envelopes, binding errors, view DDL, and nullable defaults
• lock the remaining MySQL parity work in docs/mysql-community-parity.md

Baseline

• Community contract: OtterMind/Chat2DB@3cb8af54cad5bd5caa20bb25f10d9b0e4f01931c
• Rust base: OtterMind/Chat2DB-Rust@352838b7d20fad568fd68f5d825e65c56104bd29
• original Community React frontend and styles remain unchanged

Validation

• make verify
• make native-mysql-integration MYSQL_TEST_USER=root MYSQL_TEST_PASSWORD=root
• 148 Core tests and 38 Web tests
• strict Core/Web Clippy
• real local Docker MySQL 8.4 fixture with Java deliberately dormant
• independent compatibility review with no remaining findings

Remaining

Console scripts/writes/transactions, row editing, DDL, import/export, datasource lifecycle, account administration, large-cell retrieval, original SQL utility routes, AI, CLI, and MCP conformance remain tracked in #2.

Refs #2