Add SQL Notebooks support (.exabook files)

[mikhail-zhadanov]

Summary

• SQL Notebooks — new .exabook file format for interactive SQL exploration with inline results
• JSON-based notebook format with SQL code cells and markdown documentation cells
• Cells execute against the active Exasol connection with HTML result tables
• Execution order badges, timing, row counts, cancellation support
• CodeLens "Execute" links hidden in notebook cells (native run buttons used instead)
• Demo notebook included in examples/demo.exabook

Architecture

• src/notebooks/serializer.ts — NotebookSerializer reading/writing JSON .exabook files with transientOutputs: true (results not saved to disk)
• src/notebooks/controller.ts — NotebookController executing SQL cells via existing QueryExecutor, rendering results as styled HTML tables

Test plan

• Open examples/demo.exabook — notebook renders with markdown + SQL cells
• SQL cells have Exasol syntax highlighting
• Click play on a SQL cell — results render inline as HTML table
• No "Execute" CodeLens appears inside notebook cells
• Cancel a running cell — execution stops
• Run All executes cells sequentially with execution order badges
• Create new .exabook file — opens as empty notebook
• Non-result queries (CREATE, INSERT) show success message

🤖 Generated with Claude Code

[mikhail-zhadanov]