feat: interactive data table UX — sorting, copy, EXPLAIN, column reorder

[anandgupta42]

What does this issue track?

Follow-up to PR #141 (data-focused UX polish). The initial PR shipped rich query tables, progress bars, cost badges, schema previews, type indicators, percentage bars, relative timestamps, column statistics, and boolean/NULL styling.

This issue tracks the interactive TUI features that require state management and keyboard handling — higher complexity, separate scope.

Proposed features

1. Interactive sorting — keyboard shortcuts to sort result table by column (▲/▼ indicators in header, frozen headers while scrolling)
2. Copy-to-clipboard — select cell/row/column and copy as CSV, JSON, or SQL IN clause (C/J/L shortcuts)
3. EXPLAIN plan visualization — auto-run EXPLAIN ANALYZE, render as ASCII tree with cost indicators and index usage hints (per-dialect: PostgreSQL, Snowflake, BigQuery, Databricks)
4. Column reorder + hide/show — ←/→ to reorder, H to toggle visibility, persist to session state, show "+ N hidden columns" indicator

Why

These directly address common data engineering workflows:

• Sorting: avoid rewriting ORDER BY and re-executing queries during exploration
• Copy: paste IDs into WHERE IN, copy metrics for reports, copy column names for SELECT lists
• EXPLAIN: instant performance diagnosis without leaving the tool
• Column reorder: wide result sets (20+ cols) become scannable by hiding noise

Research source

Full research in memory: competitive analysis of DataGrip, DBeaver, Snowsight, k9s, lazygit patterns. See PR #141 discussion for screenshots of the foundation these build on.

Implementation notes

• All features require interactive TUI state (keyboard event handlers, re-render on state change)
• Sorting and column reorder can share a column state management layer
• EXPLAIN is the highest complexity — requires per-dialect SQL parsing (~200 LOC per DB)
• Copy needs Node.js clipboard integration
• Each feature can be shipped independently

Checklist

• Interactive sorting with header indicators
• Copy-to-clipboard (cell, row, column, SQL formats)
• EXPLAIN plan ASCII tree visualization
• Column reorder + hide/show with session persistence