feat(mysql): complete native Console execution slice

[openai0229]

Summary

• execute unparameterized MySQL DDL/DML, queries, transactions, semicolon scripts, and DELIMITER scripts through upstream mysql_async while Java remains dormant
• preserve Community Web and desktop Console contracts, including cancellation, multiple result sets, paging, read-only enforcement, and per-statement operation history
• bound complete-script results to 64 MiB and expose owner-scoped large-value previews, chunks, and downloads
• document the resulting native Console architecture and remaining parity gaps

Baseline

• Community contract: OtterMind/Chat2DB@3cb8af54cad5bd5caa20bb25f10d9b0e4f01931c
• Rust base: OtterMind/Chat2DB-Rust@e9789cded5d227ba1f48690264046610eedb0807
• original Community React frontend and styles remain unchanged

Verification

• make verify
• make native-mysql-integration MYSQL_TEST_USER=root MYSQL_TEST_PASSWORD=*** against local MySQL 8.4
• 166 Core tests with two ignored external integrations, 40 Web tests, and 24 Desktop tests
• strict workspace Clippy, formatting, git diff --check, and Chat2DB knowledge lint
• CI run 30450042445

Commit structure

• c744341 feat(mysql): complete native console execution slice
• 056b826 docs(mysql): document native console architecture

Remaining

Table row editing and DDL, import/export and tasks, datasource lifecycle and SSH, account administration, original SQL utility routes, AI mapping, and MySQL Agent/CLI/MCP conformance remain tracked in #2.

Refs #2