feat: complete Community console with native MySQL fast path

[openai0229]

Summary

• persist saved Community consoles and expose Console APIs over web HTTP and desktop IPC
• start the Java compatibility engine only when a JDBC-only operation needs it, then stop it after the idle lease expires
• use upstream mysql_async 0.37.0 with Rustls for MySQL connection tests, metadata, table preview, and supported read-only Console SELECT
• retain the existing bounded result store, paging, operation events, cancellation, and Java fallback for unsupported databases and advanced operations
• keep macOS packaging reproducible while leaving the package workflow tag/manual only

Verification

• make verify
• make native-mysql-integration against MySQL 8.4
• cargo clippy -p chat2db-core --all-targets -- -D warnings
• actionlint .github/workflows/ci.yml
• native MySQL product test covers metadata, preview, typed SELECT, retained paging, truncation, active cancellation, unsupported-query rejection, and dormant Java assertions

Scope

• MySQL native path accepts a single parameter-free SELECT supported by the current validator
• parameterized SELECT, CTE-first SELECT, locking/server-file/multi-statement SELECT, advanced metadata, builders, writes, and non-MySQL databases remain on the compatibility path or return an explicit unsupported error before Java startup

Issue

N/A