Add Parquet file viewer with tree explorer and table view

[nwoolmer]

Summary

• Adds a custom Parquet file viewer using QuestDB's fork of the parquet2 library
• Tree view (default): hierarchical metadata explorer — file info, key-value metadata, schema with physical/logical types, row groups with column details and inline data previews
• Table view (Tab to switch): full-screen columnar data browser with horizontal scrolling and lazy row group loading
• Supports PLAIN and RLE_DICTIONARY encoding, definition levels for nullable columns, and logical type formatting (Date, Timestamp, Decimal, String, UUID)

New files

File	Lines	Purpose
src/parquet_viewer.rs	1300	Core state, tree building, page decoding
src/ui/parquet_view.rs	391	Tree and table rendering

Integration

• .parquet files are auto-detected in open_file and routed to the parquet viewer
• AppMode::ParquetViewing added with full keyboard/mouse/goto-line support
• Tree: Up/Down navigate, Enter/Right expand, Left collapse, Tab switches to table
• Table: Up/Down scroll rows, Left/Right pan columns, Tab switches to tree

Test plan

• Open a .parquet file — should show tree view with metadata
• Expand Schema, Row Groups, Columns nodes
• Expand Data Preview — should show decoded values
• Press Tab — should switch to table view with column-aligned data
• Scroll vertically and horizontally in table view
• Press q/Esc to close viewer
• Verify non-parquet files still open in text/hex viewer

🤖 Generated with Claude Code