feat: add schema clone workflow

[machado144]

Summary

• add schema clone support across CLI, TUI, and Serve
• add Serve multi-connection/preset target handling for cloning between matching DBs
• preserve preset labels, dedupe duplicate live/preset connections, and support raw connection strings
• add Serve truncate-only behavior when Rows is 0 and truncate is enabled
• document schema clone and Serve truncate-only behavior

Tests

• go test ./...
• cd integration && GOCACHE=/tmp/seedstorm-gocache /home/youngestaxe/go/bin/go1.25.10 test -v -tags integration -count=1 ./... -run 'Test(Postgres|MySQL)SchemaCloneDDL' -timeout 120s

[github-actions]

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