fix: scope MySQL list_tables to configured database

[luohui1]

Description

Scopes the MySQL list_tables query to the configured source database when one is set, so Cloud SQL MySQL prebuilt tools no longer list tables from every database in the instance.

The existing all-user-schemas behavior is preserved for sources without a configured database. This also updates the prebuilt tool descriptions and MCP schema expectation to describe the configured-database default.

PR Checklist

• Make sure you reviewed
  CONTRIBUTING.md
• Make sure to open an issue as a
  bug/issue
  before writing your code! That way we can discuss the change, evaluate
  designs, and agree on the general idea
• Ensure the tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)
• Make sure to add ! if this involve a breaking change

Testing

• go test ./internal/tools/mysql/mysqllisttables -count=1
• go test ./internal/tools/mysql/mysqllisttables -run 'TestInvokeScopesListTablesToConfiguredDatabase|TestInvokePreservesUnscopedBehaviorWithoutConfiguredDatabase' -count=1
• go test ./internal/server/mcp/jsonrpc ./internal/tools/mysql/mysqllisttables -count=1

AI disclosure: this PR was prepared by Codex (GPT-5) acting as an AI coding agent on behalf of @luohui1.

Fixes #2212

[gemini-code-assist]

Code Review

This pull request updates the list_tables tool for MySQL and Cloud SQL MySQL to scope table listing to the configured database when available, falling back to all user schemas if no database is configured. It updates the compatibleSource interface, the SQL query, and adds corresponding unit tests. The reviewer suggested using TRIM(@connected_schema) in the SQL comparison to ensure robust matching against accidental whitespace.

[gemini-code-assist]

To ensure robust matching even if the configured database name contains accidental leading or trailing whitespace (e.g., from environment variables or configuration files), use TRIM(@connected_schema) in the comparison as well, matching the TRIM used in the NULLIF check.

Suggested change

	AND (NULLIF(TRIM(@connected_schema), '') IS NULL OR T.TABLE_SCHEMA = @connected_schema)
	AND (NULLIF(TRIM(@connected_schema), '') IS NULL OR T.TABLE_SCHEMA = TRIM(@connected_schema))