Feature: Multi-statement script execution with progress

[muk2]

Summary

Add support for executing multiple SQL statements in sequence (scripts) with per-statement progress indication and individual result sets.

Motivation

Real-world database workflows often involve running multiple statements in sequence: creating tables, inserting data, running queries, and cleaning up. Currently, pgrsql splits on semicolons and executes the active block, but lacks support for running entire scripts with progress feedback.

Proposed Behavior

• Script execution: Ctrl+Shift+Enter executes all statements in the editor sequentially
• Progress indicator: Show which statement is currently executing (e.g., "Running statement 3 of 7...")
• Per-statement results: Each statement gets its own result tab, navigable with Ctrl+[/]
• Error handling: On failure, stop execution, show error with the failing statement highlighted
• Partial results: Results from successfully executed statements before the error are preserved

Acceptance Criteria

• Ctrl+Shift+Enter executes all statements sequentially
• Progress indicator shows current statement / total
• Each statement result navigable as separate tab
• Execution stops on first error
• Failing statement highlighted in editor
• Previous successful results preserved on error
• Unit tests for statement splitting logic