feat: add startup commands for connections

[datlechin]

Summary

• Add a "Startup Commands" text field in Connection > Advanced tab for running custom SQL after connecting (e.g., SET time_zone, SET search_path, SET NAMES)
• Commands execute automatically on initial connect, manual reconnect, and auto-reconnect — on both main and metadata drivers
• Fix duplicateConnection() to copy all fields (was missing sslConfig, isReadOnly, aiPolicy, and DB-specific settings)

Test plan

• Create a new connection with startup commands (e.g., SET time_zone = 'Asia/Ho_Chi_Minh'), connect, verify with SELECT @@time_zone
• Edit an existing connection to add startup commands, disconnect/reconnect, verify commands execute
• Duplicate a connection with startup commands, verify they are copied
• Test with multiple commands separated by semicolons and newlines
• Test with invalid command — verify connection still succeeds (warning logged)
• Upgrade from old config (no startupCommands field) — verify no crash
• Verify quotes stay straight in the editor (no smart quote substitution)

[chatgpt-codex-connector]

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